This article includes discussion of sleep paralysis, cataplexy of awakening, hypnagogic and hypnopompic paralysis, night palsy, nocturnal paralysis, predormital and postdormital paralysis, familial sleep paralysis, and isolated sleep paralysis. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
In this article, the authors detail the clinical and laboratory features of sleep paralysis, an intriguing REM sleep-related parasomnia found in a relevant number of otherwise normal subjects and associated but not coincidental with narcolepsy-cataplexy. Sleep paralysis may be familial and is thought to represent a disorder of REM sleep, whereby muscle atonia typical of REM sleep is concomitant with a wakeful conscious experience. The hallucinations of sleep paralysis seem to revolve around a core experience of “sensed presence” consistent with the hypothesis of REM sleep initiation of a threat-activated vigilance system.
• Sleep paralysis is a REM sleep parasomnia characterized by an inability to perform voluntary movements associated with marked anxiety that occurs either at sleep onset (hypnagogic form) or on awakening (hypnopompic form).
• Sleep paralysis attacks last a few minutes, do not involve respiratory and ocular muscles, are fully reversible, and often are accompanied by terrifying hallucinatory phenomena.
• Sleep paralysis may form part of the narcoleptic tetrad, but isolated sleep paralysis occurs independently from narcolepsy, sometimes in a familial form.
Historical note and terminology
Sleep paralysis was first described in 1876 by Mitchell, who termed it "night palsy" (Mitchell 1876); the term "sleep paralysis" was introduced by Wilson in 1928. Earlier descriptions are, however, found in the “modern” medical literature, such as the one by the Dutch physician Isbrand van Diemerbroeck in 1664 (Kompanje 2008), as well as in the “ancient” medical literature, such as that from the Persian Akhawayni in his Hidayat al-muta'allemin fi al-tibb (Learner's guide to medicine) compiled in the 10th century and others from the ancient Chinese and Greek culture (Golzari et al 2012). Literary descriptions of sleep paralysis can also be found in “The Horla” by Guy De Maupassant and in the novel Moby Dick by Herman Melville (Miranda and Högl 2013). Other names in English used to describe sleep paralysis include "nocturnal paralysis," "cataplexy of awakening," "hypnagogic and hypnopompic paralysis," and "predormital and postdormital paralysis"; in French it has been termed cataplexie du reveil. Furthermore, "Old Hag" in Canada, kanashibari in Japan, "ghost oppression" in Hong Kong Chinese, and ogun oru in Nigerians (Aina and Famuyiwa 2007) are colloquial terms employed by patients and reflect popular credence of sleep paralysis as witchcraft possession and paranormal experiences, very relevant to the issue of transcultural psychiatry (Gangdev 2006; Jacobson 2009; Jimenez-Genchi et al 2009; Jalal et al 2015). Moreover, the endorsement of a supernatural causal explanation of sleep paralysis is highly influenced by cultural and education background (Jalal et al 2014).
Adie and Wilson, in the 1920s, noted that sleep paralysis occurs frequently in narcoleptic patients. Sleep paralysis is included in the "narcoleptic tetrad" together with sleep attacks, cataplexy, and hypnagogic hallucinations, and can rarely be the first symptom of narcolepsy (Buskova et al 2013). Sleep paralysis may also occur in otherwise normal persons, a condition called "recurrent isolated sleep paralysis." The familial occurrence of isolated sleep paralysis is called "familial sleep paralysis." Recurrent isolated sleep paralysis is classified within the parasomnias usually associated with REM sleep in the current International Classification of Sleep Disorders (American Academy of Sleep Medicine 2014).
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