BASICS
- The most prevalent version of his name in literature across time thus
far is Ephialtes.
- There seems to be a lost myth in which he does indeed get into a
fight with and is defeated by a hero, none other than Herakles
[Hercules] himself. In the clearest reference to this story, the daimon's name is Epiales; and apparently after the confrontation, Epiales turns into a hedgehog.
- He is said to be a messenger, quite similar to
an angel, sent (benevolently) by the healing-god Asklepios [Asclepius]; and he is
also sometimes identified with the woodland deity Pan.
- He survives into Modern Greek folklore (as recently as the 1600s if not
later still than that) as a sort of goblin identified with certain
other boogeymen haunting the popular culture of Greece. As with the ancient Ephialtes, certain writers explain away the nightmare-visions of these creatures as merely the result of over-eating and its consequent bad digestion, or that they are just tall tales invented to mess with little kids and with the uneducated and illiterate (which, until fairly recent modern times, happens to make up the bulk of the human population).
DETAILS
There is something which appears to fit the criteria of your question precisely, but it is in German, with generous sprinklings of (completely untranslated) Ancient Greek (complete with some Latin occasionally peppered in for good measure):
Ephialtes: Eine pathologisch-mythologische Abhandlung über die Alpträume und Alpdämonen des klassischen Altertums
It was written (132 pages) by Wilhelm Heinrich Roscher and published 1900, in Leipzig, in Vol. 20 of The Treatises of the Philological-Historical Class of the Royal Saxon Society of Sciences. It is fully accessible in its entirety at the link above and is quite comprehensive.
An English translation✭ of it is available on the same website but only in Limited Book Preview form (although, as of the time of this post, it can be borrowed to be read online for an hour at a time), and the full title of which is:
Pan and the Nightmare:
Being the Only English Translation (from the German by A.V. O'Brien, M.D.) of
Ephialtes: A Pathological-Mythological Treatise on the Nightmare in Classical Antiquity,
by Wilhelm Heinrich Roscher (1900), together with
An Essay on Pan,
Serving as a Psychological Introduction to Roscher's Ephialtes,
by James Hillman
1972, Spring Publications
Beyond this, as far as my findings go, there is no single Internet source in English containing a consolidation of all the information you're looking for (at least not as of the time of this posting).
Definition-Quest
Most of the original literature mentioning the subject refers to him, or it, as Ephialtes rather than Epiales. The bulk of information on Ephialtes is in medical manuals concerned with defining and describing diseases and other ailments, accompanied by treatment instructions for them. As summarised in the short Wikipedia article "Ephialtes (illness)", this term generally refers to an anxiety disorder which causes sleep paralysis connected with dreaming:
The idea of an incubus as a causative factor in nightmares stemmed
from the belief that some spirit or ghostly person crept in during the
night and lay upon the sleeper, so as to constrict the chest and
breathing—leading to a sense of suffocation, side by side with a
terrifying dream of being either crushed or (in the case of a woman)
sexually violated by the (male) incubus or ephialtes.
In English and German
As another Wikipedia article points out, the English word nightmare itself happens to originate from "a malicious entity in Germanic and Slavic folklore that rides on people's chests while they sleep, bringing on bad dreams". In German "nightmares" are Alpträume, "elf-dreams," and Alpdrücke, "elf-oppression" or "elf-pressures," with an identical concept, in which an Alp, "elf,"
sits astride a sleeper's chest and becomes heavier until the crushing
weight awakens the terrified and breathless dreamer. The victim awakes
unable to move under the Alp's weight. This may have been an early
explanation for sleep apnea and sleep paralysis, as well as night
terrors. It may also include lucid dreams.
Roscher is also the general editor of the Ausführliches Lexikon der griechischen und römischen Mythologie, which contains a brief "Ephialtes" article differentiating among three different personages bearing this name.
The first two are two different giants, both of whom fought against the gods. Here is my translation of the main portion of the entry on the third among these characters:
a Spukgeist {"spook-spirit"} of the same kind as the incubus and
the German Alpe; he is designated as a demon and identified with
Pan... He is also called Epialtes, Epiales,
Epheles, Epopheles, and so on; Tiphys, Euopan, Baboutzikarios.
The article also cites Hesychius of Alexandria, who refers to this Spukgeist as Opheles. Book 1 of Strabo's Geography is also cited as a source, in which the author disparages the myths as merely the means by which bumpkins are indoctrinated into superstition and by which children are amused and terrified. In so saying Strabo then lists Ephialtes together with Lamia, "the Gorgon" and Mormolyke as nothing more than kid-stuff.
Tussling with Herakles
Sophron of Syracuse wrote mimes which currently survive only in fragments. The reason I refer to the story of the confrontation between Ephialtes and Herakles as a lost myth is because we know about it solely from a few of the aforementioned fragments, Numbered 68-73 (or 67-72 in a different system), which afford us only tantalisingly scant (and bizarre) detail.
Alan H. Sommerstein's 2009 book Talking About Laughter: And Other Studies in Greek Comedy (Oxford University Press) breaks it down (pp. 156-157), telling us of:
the nightmare-demon Epioles or Epiales, who suffocates (someone's? his
own?) father, but is himself suffocated by Herakles and in the
process turns, apparently, into a hedgehog. A version of Epiales
reappears, as Mastromarco among others has noted, as a victim of
Herakles-Aristophanes in Wasps 1038-9 (and also, as we shall see
later, in a comedy by Phrynichos). Mastromarco seems to equate him
with the giant Ephialtes, slain by Herakles (and Apollo) in the
Gigantomachy [21] (Apollod. 1.6.2); but there is no evidence,
literary or artistic, of any connection whatever between the Giants,
whose typical weapons are boulders and whom Herakles fights with bows
and arrows, and the nightmare-demon who chokes and is choked with bare
hands. It is quite likely that the idea of a combat between Herakles
and the folklore bogy Epiales was an invention of Sophron's, probably
inspired by the similarity of name between Ēpiales and Ĕphialtes.
The 1907 Neue Bearbeitung (Stuttgart) of Paulys Real-Encyclopädie der classischen Altertumswissenschaft contains an "Epiales" article which (in my own translation from the German) defines the personage as "a Spukdaemon {'spook-daemon'} comparable to our Alp {'elf'}" and interpreting this story as being comedic because herein "Herakles himself acts as an Alp against the Alp," rendering unto the dream-demon a taste of his own medicine.
The most relevant part of Roscher's Ephialtes to you would be pp. 52-53, wherein this story is discussed, after going through the numerous different forms of this entity's name provided by Eustathius of Thessalonica. Here is my own translation thereof:
But by far the most important thing we learn from Eustathius's note is
the myth contained in the fragment of Sophron, which shows that
Herakles was also haunted by the demon of nightmare (and fever?), but
giving tit for tat, he choked that fiend in the same way he had tried
to strangle him. As I have already explained in RhM 1898, p.
179, in this otherwise lost legend we have to see a parallel to the
battle of Herakles with Γῆρας, Old Age personified, transmitted only
through archaic artwork, or with Thanatos in Euripides' Alkestis.
Roscher then points to Illustration #5 of Plate XXXVI in Vol. 2 of Charles William King's collection Antique Gems and Rings. (See image below, followed by my translation of his description thereof.)
Perhaps that myth of Epiales and Herakles is within {this picture} ...
Herakles sits in the posture of one who is exhausted or just falling
asleep, his head and torso leaning forward, his right hand resting on
his club, on a stone (?); approaching from behind, surreptitiously, so
it would appear, is a powerful bearded man with large wings, who holds
a branch or poppy-stem in his left hand, and with his right, seems to
grasp the hero's throat as though to strangle it (cf. therefore the
definition of Ήπιάλης {Hepiales} as a demon, ὅς τοῖς κοιμωμένοις
ἐφέρπει or ἐπέρχεται in Bekk. An. 42, I & in Etym. M. 434, 5).
Similarly, Hypnos often appears in artwork as a bearded demon, usually
standing behind the sleeper, less often walking towards him, and
casting sleep from a horn above him; sometimes he touches the temples
of the weary person with a branch or poppy-stalk wet with lethaean dew;
he is often winged. It scarcely needs to be remarked that the demon of
the nightmare, which acts only in sleep or in the stage immediately
preceding it (see pp. 11 & 24), or the fever (ήπίαλος) accompanied
by restless, frightful dreams, i.e. Ήπιάλης, must from the outset
have had many things in common with Hypnos (and Oneiros).
Footnote 149 on p. 53 points out that in his Fabulae, the Roman writer Hyginus lists names of Somnia, "Dreams" (i.e. the personifications and spirits of dreams), who were born, among other entities, to Erebus (Darkness) and Nox (Night). One of these names is Epaphus, and, like several other things in Hyginus, is most likely a mistake, which Roscher says should be read as "Epialus."
He does make reference, however, to a 4-century BC magical tablet from Crete (quoted in untranslated Ancient Greek in that footnote), containing a chant saying (going by my own novice translation), "Epaphos, Epaphos, Epaphos, flee, flee along with the she-wolf (Lýkaina?), || Flee, o dog", etc. Another author, Schmidt, is cited here as interpreting Epaphos to be:
"a kind of Alp". However, as several undoubted demons in animal form
are named one after another in these verses... it is thus probable to me
that we also have to perceive in ἕπαφος {epaphos} an animal demon,
namely the hoopoe.
OTHER SOURCES
Phrynichus the Comedian
As with Sophron, the work of the comic poet Phrynichus can now be found only in scant fragmentary condition. One of the ten plays that he wrote, Sommerstein (on p. 173 of his book) tells us:
appears to have been named after the nightmare-demon Epialtes, who
in... fr. 1... appears to be addressing the audience and saying he was
given his name 'on account of his manly virtue' (ἀνδραγαθίας
οὕνεκα); it looks very much as if the audience's sympathies are to be
engaged on Epialtes' side right from the start.
And we know virtually nothing else about this theatre-piece, which I have otherwise seen generally entitled Ephialtes (rather than Epialtes).
To your Question regarding "all of the details," the most pertinent resource after Roscher's Ephialtes is the 2018 book published by Brill (Leiden & Boston), ed. Chiara Thumiger & P.N. Singer, Mental Illness in Ancient Medicine: From Celsus to Paul of Aegina. For our purposes, the book's second chapter, by Nadine Metzger, entitled '"Not a Daimōn, but a Severe Illness": Oribasius, Posidonius and Later Ancient Perspectives on Superhuman Agents Causing Disease,' is the one most applicable.
Central to your query is the second half of the chapter (pp. 94-106), which Metzger entitles "The Case of Ephialtes in Fourth-Century Medicine", and wherein (pp. 94-95) she writes:
Connections are made in all the sources between Ephialtes and
epilēpsia, and their respective attacks are considered comparable with one another—one while awake, one during sleep. Accordingly, the
late antique compilers place their comparatively short chapters on
Ephialtes directly before the much more important epilēpsia
categorising both as a sickness of the head.
Chapters on Ephialtes can be found in the medical compilations of
Oribasius (Synopsis), Aëtius of Amida, Paul of Aegina and Paulus
Nicaeus...
Paulus Nicaeus writes that many people believe Ephialtes to be a god
or daimōn whch attacks sufferers at night.
It is then pointed out that these writers' opinions differ regarding the origin of this Ephialtes, whereupon Aëtius 6.12 is cited as quoting Posidonius (pp. 95-96):
The so-called Ephialtes is no daimōn, but rather a sickness and
premonitory symptom of epilēpsia, mania and apoplēxia.
A Message of Healing from Asklepios
According to Oribasius' Synopsis 8.2 (on p. 96 of Mental Illness in Ancient Medicine):
The so-called Ephialtes is no evil daimōn, but rather on the one
hand a serious illness, and on the other hand a heavenly interpreter
and servant of Asclepius.
Metzger continues on pp. 100-101:
This "emissary of Asclepius" refers to the healing practice of
incubation, in which a cure is granted or therapeutic measures
revealed to the suffering patient through a dream vision in a shrine
to Asclepius. A dream vision could also provide insight into one's
health independently of an incubation; numerous examples of such
prognostic dreams can be found in Artemidorus' work on dream
interpretation, written in the second half of the second century CE.
As a matter of fact, Artemidorus specifically discusses Ephialtes in
his dream book. The passage places central importance on the
characteristic which defines Ephialtes in the medical sources, namely
nightmare oppression. Other than that Ephialtes is able to speak with
dreamers, give something to them, or engage them in sexual
intercourse. He can make prophecies and, most importantly, give the
sick a positive prognosis...
R.J. White's translation of Artemidorus' Oneirocritica: Interpretation of Dreams 2.37 is then quoted:
Regardless of what he does when he approaches, it signifies that the sick
will recover. For he never associates with a man who is going to die.
Regarding this, Metzger says (p. 101) that:
Similarly to Artemidorus, Oribasius' text contains the possibility of
Ephialtes having a medical-prognostic function too; his mentioning of
Asclepius as a healing god, who usually appears to sick people in
dreams to provide them with insight into their condition, implies that
his "mediator" Ephialtes fulfils the same function. Apparently,
Oribasius not only displays an open-minded attitude towards the
possibility of heavenly influence on the human body, but recognises
the healing powers of Asclepius transmitted through his emissaries...
Moreover on p. 102:
By Oribasius' time, the idea of a daimonic mediator operating between
Asclepius and the human patient has unfolded in Neoplatonic
philosophy. Primarily this cosmology tends to place higher deities
such as Asclepius far into transcendency and excludes them from
interacting with mortal materiality, generally considered to be in
opposition to the heavenly sphere. To maintain this higher deity's
influence on the world, a messenger—a daimonic intermediary—which
makes contact with the human must be assumed. This allows the
philosophically important distance between man and god to be upheld
over the course of this contact. The idea can already be found in
Plato's Symposium, in which Eros is described as intermediary
between the gods and humans (ἑρμηνεῦον καὶ διαπορθμεῦον). Daimones
are made of more material matter (ὕλη) than the gods, which allows
them to interact with the material world in a way in which the gods cannot.
This concept becomes elaborately fleshed out in Neoplatonic
demonology.
Thus Henk Versnel elaborates in his book Coping with the Gods: Wayward Readings in Greek Theology (Brill, 2011:404) that Artemidorus in this sense enumerates Ephialtes together with Hekate and Pan as "the epigegoi (terrestrial) and aisthetoi gods (who can be perceived with the senses as opposed to those through intellect only: noetoi)."
Prescriptions Against Bad Dreams
Jovan Bilbija contributes the 10th chapter, entitled "The Stuff of Dreams: Substances and Dreams in Greek and Latin Literature" (pp. 217-251) to the 2013 Routledge book Dreams, Healing, and Medicine in Greece: From Antiquity to the Present (ed. Steven Oberhelman).
According to p. 223 thereof: "In medical literature, substances for preventing bad dreams are generally medicines against ἐφιάλτης/incubus." Bilbija then summarises the basic variations of purgatives to be ingested and talismans to be worn in order to rid oneself of this ephialtes-incubus.
On p. 238 some ancient writers are quoted recommending hellebore, regarding which Bilbija says in Footnote 114:
In our passages it is the purgative black hellebore (Helleborus
cyclophyllus Boiss.); cf. C. Hünemörder, BNP, s.v. "Hellebore." The
term ἑλλέβορος was also used for Veratrum album L.
Entry A for this plant is Rufus of Ephesus apud Oribasius, Medical Questions 7.26.177:
Hellebore (ἑλλέβορος) can be administered as a purgative (καθαρτήριον)
to those who are throttled at night by a nightmare (ἐφιάλτης).
Footnote 115 (same page):
Elsewhere, Oribasius (Medical Questions 7.26.15 [p. 228, 31-p.
229, 3 Raeder]) mentions purgation as a remedy for frightening and
disturbing dreams (ἐνύπνια φοβερὰ καὶ ταραχώδη).
Entry B for the same plant (on the same page) is Oribasius, Synopsis for Eustathius 8.2 (p. 245, 10-12 Raeder):
Hellebore is especially useful to those who suffer from nightmares
(ἐφιάλτικοί). They should be given one drachma of black hellebore
(μέλας ἑλλέβορος) mixed with three obols of scammony (σκαμμωνία) and
some aromatics like anise, wild carrot, or parsley.
Hiera of Colocynth is listed next, which, according to Bilbija, denotes the Citrullus colocynthis. He quotes Scribonius Largus (100), who, writing in Latin, recommends this for "relief to those who suffer from shortness of breath, asphyxiation, and nightmare (incubo)." The Greek quotes continue (on p. 239) with more from the same above-cited section of Oribasius' Synopsis as Entry B for this plant:
The hiera of colocynth (ἡ διὰ τῆς σικυωνίασ ἱερά) is very serviceable
to those who suffer from nightmares (ἐφιάλτικοί). Patients should keep
their diet light and avoid flatulent food.
Entry C for this plant is Aëtius of Amida 6.12 (p. 152, 27-8 Olivieri):
When a person suffers from nightmares because of an unhealthy state of
the humors (κακοχυμία), one may purge him with the hiera of Archigenes
(ἡ ἱερά Αρχιγένουσ).
Footnote 124: "Aëtius provides a recipe for this hiera of colocynth at 3.115 (p. 304, 9-16 Olivieri)."
And that covers all of the "Other references not currently quoted" on your Theoi.com Epiales page, except for the following, also listed in Dreams, Healing, and Medicine in Greece.
Dioscorides 3.140:
Drinking 15 black grains (κόκκοι) of peony (γλυκισίδη) with hydromel
or wine will help those who are throttled (οἱ πνιγόμενοι) by
nightmares (ἐφιάλται). It also helps those with stomach problems and
it relieves women with a suffocating or painful womb.
Dioscorides, On Simple Medicines 1.28:
Those who are often suffocated by nightmares (οἱ ὑπὸ τῶν ἐφιαλτῶν
πνιγόμενοι) are healed by frequent drinks of a mixture of 15 black
grains of peony (γλυκισίδη) with water.
Oribasius, Synopsis for Eustathius 8.2 (p. 245, 13-15 Raeder):
Those who suffer from nightmares (ἐφιάλτικοί) will benefit from
frequently drinking 15 pounded grains of peony (παιωνία) with water.
Based on those, if one were to make up a single English word for the victims of Ephialtes (rather than the translation "those who suffer from nightmares"), it should probably be "ephialtics" (cf. epileptics).
This is Francis Adams' 1844 translation of Paul of Aegina 3.15 (with my own emphasis):
Some say that this disorder is called ephialtes in Greek, from
the name of a man, or from those in it fancying as if one leaped upon
them. But Themison, in the tenth book of his Epistles, calls it
pnigaleon, from a Greek word signifying suffocation. It attacks persons after a surfeit, and who are labouring under protracted
indigestion. Persons suffering an attack experience incapability of
motion, a torpid sensation in their sleep, a sense of suffocation, and
oppression, as if from one pressing them down, with inability to cry
out, or they utter inarticulate sounds. Some imagine often that they
even hear the person who is going to press them down, that he offers
lustful violence to them, but flies when they attempt to grasp him
with their fingers. The evil must be guarded against at the
commencement; for when it continues long, and attacks every night, it
is the forerunner of some serious disease, such as apoplexy, mania, or
epilepsy, when the exciting cause is determined to the head; for such
as persons affected with epilepsy are, during the day, those labouring
under nightmare are in their sleep. We must evacuate the patient's
general system by opening a vein and administering purgatives. Black
hellebore is especially serviceable to such persons when given to the
amount of a drachm, if three oboli of scammony, and some of the
aromatics, such as anise, wild carrot, and Macedonian parsley, be
mixed with it. The composition called hiera, from wild gourd, is also
of great service; it is the hiera of Ruffus. The diet should be light,
and they ought to avoid everything that is flatulent. They are
benefited also by the fruit of peony: fifteen of the black grains of
which may be pounded with water and drunk frequently.
Adams provides some supplementary details in his Commentary on this chapter on p. 389 of Vol. 1 of The Seven Books of Paulus Ægineta.
Identification with Modern Ghouls
The Suda entry "Ephialtes" says that he is "the one called by many Baboutzikarios" just before a second definition: "The vapour which rises into the head, caused by overeating and indigestion, is called ephialtes by physicians."
Evy Johanne Håland says in her book Competing Ideologies in Greek Culture, Ancient and Modern (Cambridge Scholars Publishing, 2019:119) that the Baboutzikarios is said to be of Slavic origin. This would then dovetail with our English night-mare, which as we have already observed (see the "In English and German" section of this Answer) above, also has a Slavic connection.
Leo Allatius published a sort of cultural guidebook in 1645, which Karen Hartnup expounds upon in her own 2004 book which incorporates the title of his text into its own: 'On the Beliefs of the Greeks': Leo Allatios and Popular Orthodoxy (Brill: Leiden & Boston).
Hartnup reports the following about Allatius' narration of some of the practices of his fellow Christian Greeks in the 1600s (pp. 29-30, with my own emphasis):
In chapter X Allatios accepts Psellos' interpretation of the
babutzikarios, a kind of frightening goblin that is supposed to appear over the Christmas period... Even though such demons do not
exist, people actually see the demonic beings but this is
because of hallucinations brough about by over-indulgence in the
seasonal festivities. Allatios points out that this exotiko is not
always understood this way. The Byzantine dictionary Suidas
describes the babutzikarios in terms of ephialtes — a nightmare
brought on by indigestion. However, the 'common people' continue to
believe that those born at Christmas are every year possessed by the
devil during this week and attack people on the roads, asking 'Rope or
lead?' Those who reply 'Lead', the possessed person crushes to death;
those who reply 'Rope', he sets free. The Greeks distract the
possessed over the Christmas season by making them count the holes in
a sieve. This kind of babutzikarios is identical to the creature
called by others 'kallikantzaros', which is the focus of Allatios'
next chapter...
Kallikantzaroi are also goblin-like creatures that appear
between Christmas and the New Year. People try to ward them off by
wearing new clothes and the population of Chios believes that they
congregate in wooded and inaccessible places, where those of unsound
mind are also thought to originate. In order to prevent those born
between Christmas and New Year becoming kallikantzaroi they burn the
soles of their feet and remove their nails.
Endnote
✭ Which comes to my attention courtesy of tblue, a fellow Mythology StackExchange user.
