Saturday, 10 May 2014

An Introduction to Sleep Paralysis

Since I had a nasty sleep paralysis experience a little while ago (see Dream 216 by clicking on this link), I thought it was about time that I wrote an article about it. Sleep paralysis is a phenomenon which typically occurs when a person is either waking or falling asleep and experiences a temporary inability to move their body or use their voice. Researchers have found that two brain chemicals - glycine and GABA - are responsible for muscle paralysis during episodes of sleep paralysis. 

It has been characterised as a temporary state during the transition between sleep and wakefulness which is marked by muscle atonia (weakness) and may be accompanied by terrifying hallucinatory visions or audible sounds, to which the person is unable to react. Many sufferers of sleep paralysis describe experiences of being visited by a spirit, demon or entity, which either physically attacks them, sits on them restricting breathing or movement, or tries to have sex with them. These experiences may also be accompanied by feelings of floating, falling or dissociating from the physical body. Typically, the sensory elements of sleep paralysis are considered to be more distressing and traumatic than mere paralysis. Studies have shown that sleep paralysis has a more negative impact on 'intuitive thinkers' who hold supernatural beliefs regarding the cause, and perceive the experience as 'threatening' in contrast to 'analytical thinkers' who explain their sleep paralysis experience in scientific or naturalistic terms. However, studies have been unable to draw any causal relationship between beliefs and frequency of sleep paralysis occurrence. Oneironauts and lucid dreamers may actually welcome episodes of sleep paralysis as it is regarded as a good gateway to lucidity and OBEs (out-of-body experiences).

Scientists believe that sleep paralysis occurs as a result of interrupted REM sleep. The REM stage of sleep - in which dreaming occurs - puts the sleeper into a state of paralysis to prevent them from acting out their dreams. Sleep paralysis has been linked to a number of disorders including sleep apnea, narcolepsy, migraines and anxiety, but it can also occur in isolation of any other sleep-related issue. 

The two main forms of sleep paralysis are isolated sleep paralysis (ISP) and recurrent isolated sleep paralysis (RISP) - with ISP being the more common type experienced. Occurrences of ISP tend to be infrequent and short in duration - typically lasting less that one minute. ISP may only occur once in an individual's entire life. They tend to be associated with incubus/intruder hallucinations. RISP is a chronic form of the phenomenon, where the individual will suffer frequent occurrences which  much longer - sometimes for as long as one hour at a time - and also experience perceived out of body experiences. In cases of RISP, some individuals will experience numerous incidents of sleep paralysis throughout the course of a single episode of sleep. Apparently, it is difficult to distinguish between narcoleptic cataplexy and sleep paralysis, as the two conditions are physically indistinguishable. However cataplexy most commonly occurs when an individual is falling asleep, while ISP and RISP tend to occur when the individual is waking. 

Approximately 30 - 50% of individuals diagnosed with narcolepsy experience sleep paralysis as an auxiliary symptom, compared with around 6.2% of the general population. Some studies suggest that between 5 - 60% of the general population experiences episodes of sleep paralysis, but these figures vary significantly due to survey method differences. The majority of individuals who experience non-narcoleptic sleep paralysis will have a episode once a month to once a year. Only 3% of individuals prone to sleep paralysis and who are not diagnosed with a neurological or sleep disorder will experience RISP on a nightly basis. There is no known gender bias revealed by research, although age has been found to be a factor, with certain age groups being more susceptible - around 36% of individuals who experience ISP will do so between the ages of 25 - 44 years.

The pathophysiology of sleep paralysis has not been clearly identified, although several theories have been put forward as explanation. The first - and most common - of these theories suggests that sleep paralysis is a form of parasomnia which results from an abnormal overlap between REM sleep stages and wakefulness. Polysomnographic studies have shown that individuals suffering from sleep paralysis had shorted REM latencies and REM/NREM cycles than normal, as well as fragmented REM stages. This study supports the notion that disturbance of regular sleep patterns can instigate an episode of sleep paralysis as this disturbance can cause fragmentation of REM cycles - a state often observed in combination with sleep paralysis.

Another theory of sleep paralysis suggests it may occur because the neural bodies responsible for the regulation of sleep are out of balance, which causes the sleep states to overlap. The sleep-on (cholinergic neural populations) are over-activated and the sleep-off (serotonergic neural populations) are under-activated, and the latter - which enable complete arousal from the sleep state - cannot overcome the former, which keep the brain in a state of sleep. During normal REM sleep, the threshold for stimuli to cause arousal is elevated significantly, contrasted with sleep paralysis states, where there is no blocking of exogenous stimuli, which means it is much easier for an outside stimulus (such as noise) to arouse the sleeper. It is also argued that there may be problems in melatonin regulation, which in normal circumstances regulates serotonergic neural populations. Melatonin is typically at its lowest point during REM sleep. Inhibition of melatonin at an inappropriate time makes it impossible for the sleep-off neural populations to de-popularise when presented with a stimulus which would normally result in complete arousal (such as the sound of an alarm clock). This explains how REM sleep and waking states may overlap, and the sensation of muscle paralysis upon waking. If the effects of sleep on neural populations cannot be counteracted, then the characteristics of REM sleep are retained in waking states, with common consequences being anxiety/paranoia, muscle pain/weakness and headaches.

Research into sleep paralysis has found a genetic link - the characteristic fragmentation of REM sleep, hypnopompic and hynagogic hallucinations have a hereditary component in other parasomnias which lends credence to the idea that sleep paralysis may be inherited. Twin studies of monozygotic pairs (identical twins) have shown that if one twin experiences sleep paralysis (RISP), the other twin is also likely to also.

Theories of sleep paralysis which support the genetic argument, tend to point to disruption at the physiological level as an explanation - i.e. mistakes in the signalling pathways for arousal or disruption of melatonin/neural population regulation. broader diagnoses focus on the dissociative elements as being key to explaining the phenomenon, pointing towards studies into narcoleptics, who have difficulty in recall and distinguishing between waking/sleep states and dreaming/reality, which are also characteristic of states of delirium. There has also been suggestion that sleep paralysis may be positively correlated with depression, as there is an 11% frequency of sleep paralysis observed in depressive individuals which may indicate that sleep paralysis is caused by a disruption in REM sleep, triggered by depressive states.

Sleep paralysis is diagnosed by ruling out the presence of other sleep disorders, such as narcolepsy, for which there is a genetic test available. There are many potential ways to prevent sleep paralysis advocated, such as refraining from behaviours thought to be linked to the phenomenon, or changing sleeping routines believed to contribute to its occurrence. Studies have linked insomnia, sleep deprivation, disruption of sleep patterns, over-use of stimulants, use of certain ADHD medications, physical fatigue and stress to a greater likelihood of sleep paralysis occurring. Sleeping in the supine position (laying on the back, face up) is also a prominent instigator of sleep paralysis, largely because this position makes it easier for the soft palate to collapse and obstruct the airways of the sleeper, which is a possibility even in individuals not diagnosed as suffering from sleep apnea. The increased exertion of pressure from gravity on the lungs may be responsible for a greater amount of micro-arousals during sleep. 

Many factors can therefore increase the risk of RISP and ISP, but these conditions can often be avoided by making minor lifestyle changes, for example, adopting regular sleep routines and good 'sleep hygiene' although theories which support genetic causes of sleep paralysis would dispute the effectiveness of environmental changes in prevention and this explains why sleep paralysis persists in some individuals.

Cross-cultural explanations for sleep paralysis

Samuel Johnson codified sleep paralysis as a 'nightmare' in A Dictionary of the English Language (1755). Sleep paralysis is attributed to the work of demons, specifically incubi, which were said to sit on the chest of sleepers. The old English name for these beings was 'mare' or 'maere' (from proto-German 'maron', which is similar to the Sanskrit word of the same spelling and old Norse 'mara' which is reminiscent of the Greek word which appears in the Odyssey) - hence nightmare. Many European cultures have variants of this belief/word: in Iceland, Sweden, the Faroe Islands, Bulgaria and Poland, the term 'mara' is used; in Germany 'mahr'; In Holland 'nachmerrie'; in Denmark and Norwich 'mare'; in Old Irish 'morrigain'; in Croatia, Bosnia, Serbia and Slovenia 'mora'; in French 'cauchemar'; in Romania 'moroi'; in the Czech Republic 'mura'; and in Slovakia 'mora'. The origin is thought to date back to the proto-Indo-European era where reference is made to  'mora' or 'mer' which means 'harm' or 'to rub away'.

Folklore suggests that spiritual possession or magic could be the cause of sleep paralysis, whilst by the 19th century, Europeans were considering dietary habits as a potential explanation for sleep paralysis - for example Charles Dicken's A Christmas Carroll (1843) and The Household Cyclopedia (1881) both refer to various foods as reasons for dream disturbances.

In Scandinavian folklore, sleep paralysis is caused by a 'mare' which is a damned, cursed woman, related to inbuci and succubi. She leaves her physical body at night and visits sleepers, sitting on their ribcage, leading to them experiencing sleep paralysis. This theme is explored in the Swedish movie Marianne (2011). Finnish culture refers to sleep paralysis as 'unihalvaus', although the word for nightmare, 'painajainen' is thought to originally refer to sleep paralysis - 'painajai' means 'pusher/presser'.

In Hungarian society, the 'lidercnyomas' refers to both 'pressing' and 'wraith'. Other phrases used to explain sleep paralysis are 'boszorkany' (witch), 'tunder' (fairy) or 'ordogszereto' (demon lover). In Iceland, sleep paralysis is said to be caused by a 'mara' - a female goblin or succubus.

In Malta, sleep paralysis is caused by an attack by Haddiela - the wife of Hares, a mythological character. The Haddiela attacks in a similar way to that attributed to poltergeists and can be prevented by placing a knife or silverware under the pillow prior to sleep. In Greece and Cyprus, sleep paralysis is caused by mora, 'vahnas' or 'varypnas' which visit the sleeper to steal their speech and sit on their chest, causing a sensation of asphyxiation.

Catalan culture interprets sleep paralysis as visitation by a giant cat or dog which is covered in black hair and has steel paws (with holes, so the 'pesanta' as it is known,  is unable to steal anything). It sits on the chest of the sleeper.

In Latvia, sleep paralysis is caused by the 'lietuvens', the soul of a person killed by strangulation, hanging or drowning. It visits the sleeper and domestic animals and strangles/tortures its victim, although it can be overcome by moving the big toe of the left foot.

In Newfoundland (South Carolina) and Georgia, local mythology tells of an old hag, who leaves her physical body at night and sits on the chest of sleepers, causing sleep paralysis. The hag is thought to be summonsed by curse for the purposes of attacking a third party. In David J Hufford, The Terror that Comes in the Night (1982), the author states that it is local custom to recite the Lord's Prayer backwards to repel the hag.

In Gullar lore, the experience of nightmares is referred to as being 'hag-ridden'. The 'old hag' figure appears in old English and Anglo-American custom, as a nightmare spirit. In the Southern states of the USA, old custom would refer to a 'witch riding your back' as an explanation of sleep paralysis. It is considered to be a portent of forthcoming tragedy or accident.

It is now believed that reporting of nocturnal attacks by 'witches' such as Bridget Bishop during the Salem Witch Trials (1692 - 1693) were probably incidences of sleep paralysis.

In Mexico, sleep paralysis is thought to be caused by 'subirse el muerto' ('dead person on you') while in Brazil, local custom refers to a mythological being called the 'pisadeira' which means 'she who steps on someone's back'.

Independent research studies have found that African-Americans tend to be more predisposed to ISP, referring to the experience as a 'witch/haint riding you'. In contemporary Western culture, reference is made to 'shadow people', typically identified as three separate entities: a man with a hat, an old hag and a hooded figure. The presence of these characters are explained by statistics which suggest that 20% of sleep paralysis occurrences involve hallucinations. This could also provide an explanation for perceived alien abductions.

In Fiji, sleep paralysis is described as 'kana tevoro' or 'being eaten by a demon'. The demon is often interpreted as being the recently deceased relative of the sleeper who has returned due to unfinished business or to communicate something important to the sleeper. It is typical for the sleep paralysis sufferer to shout 'kania!' to the demon, which means 'eat!' - encouraging the 'possession' to be prolonged so the sleeper might seek answers to why the demon has come to them. Upon awakening from the sleep paralysis, the demon is cursed with expletives and chased away.

In Nigeria, ISP is much more common in individuals of African descent than Nigerian Africans or white persons, and is referred to as having 'the devil on your back'. Amongst the Yoruba people of Southern Nigeria, sleep paralysis is thought to be caused by 'Ogun Oru' ('nocturnal warfare') which involves acute night-time disturbance, attributed to demonic infiltration of the body and psyche of the sleeper whilst dreaming and characterised by a female presence - a 'spiritual spouse' in a feud with the dreamer's 'earthly spouse' whom appears due to eating whilst dreaming, causing bewitchment of the sleeper. The condition is treated by Christian prayer or elaborate ritual to exorcise the imbibed demonic spirit. In Zimbabwe, sleep paralysis is known as 'Madzikirira' which means 'something pressing one down' and is characterised as an evil spirit who visits the sleeper to use them for a malevolent purpose. In Ethiopia, the word 'dukak' is used to describe sleep paralysis - an evil spirit which visits the sleeper. Long-term chewers of khat often experience sleep paralysis as a side-effect of withdrawal. 'Dukak' used in the context of khat use translates as 'depression' - which afflicts those quitting khat. The dukak is perceived as an anthropomorphism of the depressive state, who appears in hallucinations and physically tortures its victims. In Swahili-speaking East African cultures, sleep paralysis is referred to as 'jinamizi' - a creature which sits on the sleeper, sometimes strangling them, and making it difficult to breath. In Morocco, sleep paralysis is known as 'Bou Rattat' - a demon which covers the sleeper's body so they are unable to move or speak.

In Turkey, sleep paralysis is known as 'karabasan' which is a form of demonic visitation during sleep. A 'djinn' (Arabic, 'cin' in Turkish, 'genie' in English) holds the sleeper down and strangles them so it can steal their breath, only relenting if their victim prays to Allah and recites certain passages of the Qur'an. In both Pakistani and Iranian cultures, sleep paralysis is explained by a visit from 'Shaitan' (Satan), 'bakhtak' or 'ifrit' which is a ghoulish haunting caused by the black magic or curses of an enemy. Many persons wear a 'ta'wiz' amulet to ward off the evil eye and Muslim holy men are able to perform exorcism in the event of such a curse being placed on a person or household. Arabic cultures also refer to the 'Ja thoom' which translates as 'what sits heavy on something' and is attributed to visitation by the Shaitan or ifrit sitting on the sleeper's chest, which can be prevented by sleeping on the right side and reading the Throne Verse of the Qur'anKurdish folklore refers to the 'Motakka', a demon which visits sleepers to steal their breath. It is believed that young children are particularly targeted because they tend to breath heavier during sleep.

In Thailand Laos and Cambodia, folklore says that sleep paralysis is caused by a ghost known as 'Phi Am', a popular character in Thai comics, who assaults the sleeper severely enough to cause bruising. Sleep paralysis is sometimes referred to as 'khmout sukkhot' and is distinct from other types of ghost possession. 

In Hmong lore, sleep paralysis is referred to as 'dab tsog' which is a nocturnal pressing spirit who holds the sleeper down and has been blamed for incidence of sudden unexplained nocturnal death syndrome (there were over 100 sudden nocturnal deaths of South East Asians between the 1970s and 1980s, but this is now believed to be the result of Brugada syndrome, a genetic cardiac disorder following studies of the interplay between this condition and the traditional meaning of the 'dab tsog' attack).

In Vietnam, sleep paralysis is known as 'ma de' ('being held down by a ghost') or 'bong de' ('being held down by a shadow'). In the Phillipines 'bangungut' is an experience of sleep paralysis attributed to nightmares which are capable of killing the sleeper. In Malaysian custom, 'kena tindh' (or 'ketindihan in Indonesian) refers to 'being pressed' and this experience is believed to be the result of malign presence in the guise of demonic figures which appear in the 'blind spot' of a person's field of vision.

In Eastern Chinese custom, it is thought that a mouse can steal your breath at night in order to give it longevity and take human form at night. The mouse is believed to achieve this by sitting on the sleeper's face, usually under their nostrils. In other Chinese lore, sleep paralysis or (gui ya shen/chuang or 'meng yan' is described as 'ghost pressing on body', 'ghost pressing on bed' or 'ghost oppression').

In Japanese culture, sleep paralysis is known as 'kanashibari', meaning 'bound or fastened in metal'. In Korea, the term for sleep paralysis is 'gawi nulim' which means 'being pressed down by a ghost'. In Mongolia, sleep paralysis is called 'khar darakh' which translates as 'to be pressed by the Black' or 'when the Dark presses'.

In Kashmiri tradition, sleep paralysis is caused by an invisible being known as a 'pasokdhar' or 'sayaa' which resides in every house, but makes its presence known if the house is unclean or the inhabitants have failed to worship every god. 

In Bangladesh, sleep paralysis is referred to as 'boba' which literally translates to 'speechless' - one of the common symptoms of sleep paralysis. In Tamil Nadu and Sri Lanka, sleep paralysis is referred to as 'Amuku Be' or 'Amuku Pei' which means 'ghost that forces one down'). In Nepalese and especially Newari tradition, sleep paralysis is caused by 'Khyaak' which is a ghost which lives in the dark places under the stairs.

I plan to post further articles on this topic as there is a wealth of information, particularly on the relationship between sleep paralysis and lucid dreaming. In the meantime, please enjoy some images inspired by accounts of sleep paralysis which I have posted below. I have included the details of the artist/title/date where possible.
Eugene Thivier, Le Cachemar (1894)
Henry Schreiber, Night Terror (2012)
Nikolai Abraham, Abildgaard, Mareridt (1800)
Henry Fuselli, The Nightmare (1781)


  1. I enjoyed reading this article. PLease continue publishing helpful topics like this. Regards, from beddingstock

  2. Interesting reading. I have suffered sleep paralysis in the past on a number of occasions. I liked your reference to the Latvian demon, Lietuvēns. I've written a novella entitled "Lietuvēns" which is being released in weekly episodes via my blogsite:

    It's actually a tale of fighting corruption in Latvia, but Lietuvēns is the narrator!