Sleep paralysis

A picture of a succubus-like vision, in contrast to the incubus. My Dream, My Bad Dream, 1915, by Fritz Schwimbeck

Several types of hallucinations have been linked to sleep paralysis: the belief that there is an intruder in the room, the presence of an incubus, and the sensation of floating.[14] A neurological hypothesis is that in sleep paralysis the mechanisms which usually coordinate body movement and provide information on body position become activated and, because there is no actual movement, induce a floating sensation.[14]

The intruder and incubus hallucinations highly correlate with one another, and moderately correlated with the third hallucination, vestibular-motor disorientation, also known as out-of-body experiences,[14] which differ from the other two in not involving the threat-activated vigilance system.[18]

A hyper-vigilant state created in the midbrain may further contribute to hallucinations.[8] More specifically, the emergency response is activated in the brain when individuals wake up paralyzed and feel vulnerable to attack.[14] This helplessness can intensify the effects of the threat response well above the level typical of normal dreams, which could explain why such visions during sleep paralysis are so vivid.[14] The threat-activated vigilance system is a protective mechanism that differentiates between dangerous situations and determines whether the fear response is appropriate.[14]

The hyper-vigilance response can lead to the creation of endogenous stimuli that contribute to the perceived threat.[8] A similar process may explain hallucinations, with slight variations, in which an evil presence is perceived by the subject to be attempting to suffocate them, either by pressing heavily on the chest or by strangulation.[14] A neurological explanation holds that this results from a combination of the threat vigilance activation system and the muscle paralysis associated with sleep paralysis that removes voluntary control of breathing.[14] Several features of REM breathing patterns exacerbate the feeling of suffocation.[14] These include shallow rapid breathing, hypercapnia, and slight blockage of the airway, which is a symptom prevalent in sleep apnea patients.[8]

According to this account, the subjects attempt to breathe deeply and find themselves unable to do so, creating a sensation of resistance, which the threat-activated vigilance system interprets as an unearthly being sitting on their chest, threatening suffocation.[8] The sensation of entrapment causes a feedback loop when the fear of suffocation increases as a result of continued helplessness, causing the subjects to struggle to end the SP episode.[14]

Episodes of sleep paralysis can occur in the context of several medical conditions (e.g., narcolepsy, hypokalemia). When episodes occur independent of these conditions or substance use, it is termed "isolated sleep paralysis" (ISP).[19] When ISP episodes are more frequent and cause clinically significant distress or interference, it is classified as "recurrent isolated sleep paralysis" (RISP). Episodes of sleep paralysis, regardless of classification, are generally short (1–6 minutes), but longer episodes have been documented.[8]

It can be difficult to differentiate between cataplexy brought on by narcolepsy and true sleep paralysis, because the two phenomena are physically indistinguishable. The best way to differentiate between the two is to note when the attacks occur most often. Narcolepsy attacks are more common when the individual is falling asleep; ISP and RISP attacks are more common upon awakening.[18]

Similar conditions include:

• Exploding head syndrome (EHS) potentially frightening parasomnia, the hallucinations are usually briefer always loud or jarring and there is no paralysis during EHS.[21]
• Nightmare disorder (ND); also REM-based parasomnia[21]
• Sleep terrors (STs) potentially frightening parasomnia but are not REM based and there is a lack of awareness to surroundings, characteristic screams during STs.[21]
• Noctural panic attacks (NPAs) involves fear and acute distress but lacks paralysis and dream imagery[21]
• Posttraumatic stress disorder (PTSD) often includes scary imagery and anxiety but not limited to sleep-wake transitions[21]

Though no large trials have taken place which focus on the treatment of sleep paralysis, several drugs have promise in case studies.[25] Two trials of GHB for people with narcolepsy demonstrated reductions in sleep paralysis episodes.[25]

Pimavanserin has been proposed as a possible candidate for future studies in treating sleep paralysis.[26]

Some of the earliest work in treating sleep paralysis was done using a cognitive-behavior therapy called CA-CBT. The work focuses on psycho-education and modifying catastrophic cognitions about the sleep paralysis attack.[27][28] This approach has previously been used to treat sleep paralysis in Egypt, although clinical trials are lacking.[29]

The first published psychosocial treatment for recurrent isolated sleep paralysis was cognitive-behavior therapy for isolated sleep paralysis (CBT-ISP).[19] It begins with self-monitoring of symptoms, cognitive restructuring of maladaptive thoughts relevant to ISP (e.g., "the paralysis will be permanent"), and psychoeducation about the nature of sleep paralysis. Prevention techniques include ISP-specific sleep hygiene and the preparatory use of various relaxation techniques (e.g. diaphragmatic breathing, mindfulness, progressive muscle relaxation, meditation). Episode disruption techniques[30] are first practiced in session and then applied during actual attacks. No controlled trial of CBT-ISP has yet been conducted to prove its effectiveness.

A 19th century version of Füssli's The Nightmare (1781)

The original definition of sleep paralysis was codified by Samuel Johnson in his A Dictionary of the English Language as nightmare, a term that evolved into our modern definition. The term was first used and dubbed by British neurologist, S.A.K. Wilson in his 1928 dissertation, The Narcolepsies.[33] Such sleep paralysis was widely considered the work of demons, and more specifically incubi, which were thought to sit on the chests of sleepers. In Old English the name for these beings was mare or mære (from a proto-Germanic *marōn, cf. Old Norse mara), hence comes the mare in the word nightmare. The word might be cognate to Greek Marōn (in the Odyssey) and Sanskrit Māra.

Le Cauchemar (The Nightmare), by Eugène Thivier (1894)

Although the core features of sleep paralysis (e.g., atonia, a clear sensorium, and frequent hallucinations) appear to be universal, the ways in which they are experienced vary according to time, place, and culture.[9][34] Over 100 terms have been identified for these experiences.[19] Some scientists have proposed sleep paralysis as an explanation for reports of paranormal phenomena such as ghosts,[35][36] alien visits,[37] demons or demonic possession,[9][38] alien abduction experiences,[39][40] the night hag and shadow people haunting.[11][14]

According to some scientists culture may be a major factor in shaping sleep paralysis.[38] When sleep paralysis is interpreted through a particular cultural filter, it may take on greater salience. For example, if sleep paralysis is feared in a certain culture, this fear could lead to conditioned fear, and thus worsen the experience, in turn leading to higher rates.[9][38] Consistent with this idea, high rates and long durations of immobility during sleep paralysis have been found in Egypt, where there are elaborate beliefs about sleep paralysis, involving malevolent spirit-like creatures, the jinn.[38]

Research has found that sleep paralysis is associated with great fear and fear of impending death in 50% of sufferers in Egypt.[38] A study comparing rates and characteristics of sleep paralysis in Egypt and Denmark found that the phenomenon is three times more common in Egypt versus Denmark.[38] In Denmark, unlike Egypt, there are no elaborate supernatural beliefs about sleep paralysis, and the experience is often interpreted as an odd physiological event, with overall shorter sleep paralysis episodes and fewer people (17%) fearing that they could die from it.[34]

The night hag is a generic name for a folkloric creature found in cultures around the world, and which is used to explain the phenomenon of sleep paralysis. A common description is that a person feels a presence of a supernatural malevolent being which immobilizes the person as if standing on the chest.[41] This phenomenon goes by many names.

In Egypt, sleep paralysis is conceptualized as a terrifying jinn attack. The jinn may even kill its victims.[34]

Sleep paralysis among Cambodians is known as “the ghost pushes you down,”[36] and entails the belief in dangerous visitations from deceased relatives.[36]

In the different regions of Italy there are many examples of supernatural beings associated with sleep paralysis. In the regions of Marche and Abruzzo, it is referred to as a Pandafeche attack;[9] the Pandafeche usually refers to an evil witch, sometimes a ghostlike spirit or a terrifying catlike creature, that mounts on the chest of the victim and tries to harm him. The only way to avoid her is to keep a bag of sand or beans close to the bed, so that the witch will stop to count how many beans or sand-grains are inside it. A similar tradition is present in the Sardinian folklore, where the Ammuntadore is known as a creature that mounts on the people's chest during their sleep to give them nightmares, and that can change its shape according to the person's fears. In Northern Italy, specifically in the Tyrol area, the Trud is a witch that sits on the people's chest at night, making them unable to breath; to chase her away, people should make the sign of the Cross, something that would need a great struggle in a situation of paralysis.[42] In Southern Italy, sleep paralysis is usually explained with the presence of a sprite standing on the people's chest: if the person manages to catch the sprite (or steal his hat), in exchange for his freedom (or to have his hat back) he can reveal the hiding place of a rich treasure; this sprite has different names in different regions of Italy: Monaciello in Campania, Monachicchio in Basilicata, Laurieddhu or Scazzamurill in Apulia, Mazzmuredd in Molise.[43]

In Newfoundland, sleep paralysis is referred to as the Old Hag,[35][44] and victims of a hagging are said to be hag-ridden upon awakening.[45] Victims report being completely conscious, but unable to speak or move, and report a person or an animal which sits upon their chest.[46] Despite the name, the attacker can be either male or female.[47] Some suggested cures or preventions for the Old Hag include sleeping with a Bible under the pillow,[46] calling the sleeper's name backwards[48] or in an extreme example, sleeping with a shingle or board embedded with nails strapped to the chest.[49] This object was called a Hag Board.[50] The Old Hag is well-enough known in the province to be a pop culture figure, appearing in films and plays[51] as well as in crafted objects.[52]

Sleep paralysis is sometimes interpreted as space alien abduction in the United States.[53]

Various forms of magic and spiritual possession were also advanced as causes in literature. In nineteenth century Europe, the vagaries of diet were thought to be responsible. For example, in Charles Dickens's A Christmas Carol, Ebenezer Scrooge attributes the ghost he sees to "... an undigested bit of beef, a blot of mustard, a crumb of cheese, a fragment of an underdone potato..." In a similar vein, the Household Cyclopedia (1881) offers the following advice about nightmares:

"Great attention is to be paid to regularity and choice of diet. Intemperance of every kind is hurtful, but nothing is more productive of this disease than drinking bad wine. Of eatables those which are most prejudicial are all fat and greasy meats and pastry... Moderate exercise contributes in a superior degree to promote the digestion of food and prevent flatulence; those, however, who are necessarily confined to a sedentary occupation, should particularly avoid applying themselves to study or bodily labor immediately after eating... Going to bed before the usual hour is a frequent cause of night-mare, as it either occasions the patient to sleep too long or to lie long awake in the night. Passing a whole night or part of a night without rest likewise gives birth to the disease, as it occasions the patient, on the succeeding night, to sleep too soundly. Indulging in sleep too late in the morning, is an almost certain method to bring on the paroxysm, and the more frequently it returns, the greater strength it acquires; the propensity to sleep at this time is almost irresistible."[54]

J. M. Barrie, the author of the Peter Pan stories, may have had sleep paralysis. He said of himself ‘In my early boyhood it was a sheet that tried to choke me in the night.’[55] He also described several incidents in the Peter Pan stories that indicate that he was familiar with an awareness of a loss of muscle tone whilst in a dream-like state. For example, Maimie is asleep but calls out ‘What was that....It is coming nearer! It is feeling your bed with its horns-it is boring for [into] you’.[56] and when the Darling children were dreaming of flying, Barrie says ‘Nothing horrid was visible in the air, yet their progress had become slow and laboured, exactly as if they were pushing their way through hostile forces. Sometimes they hung in the air until Peter had beaten on it with his fists.’[57] Barrie describes many parasomnias and neurological symptoms in his books and uses them to explore the nature of consciousness from an experiential point of view.[58]

The Nightmare is a 2015 documentary that discusses the causes of sleep paralysis as seen through extensive interviews with participants, and the experiences are re-enacted by professional actors. In synopsis, it proposes that such cultural phenomena as alien abduction, the near death experience and shadow people can, in many cases, be attributed to sleep paralysis. The "real-life" horror film debuted at the Sundance Film Festival on January 26, 2015 and premiered in theatres on June 5, 2015.[59]