My limbs won’t move. I can’t scan the room or, more importantly, run if I needed to. This feeling in itself is terrifying, but I become aware of an evil presence in the room. It’s behind me and is waiting there. All I’m aware of is a jagged shadow which means me some ill. I’m desperate to move, to escape, to scream out and run from this figure watching me. Minutes pass and my focus is on moving, willing my failing limbs to spring into action. Suddenly they return back to life and I instinctively look towards the corner of the room where I felt a malevolent being was sizing me up. There’s nothing there but darkness and my old blue wooden wardrobe. Shaken and tired, I attempt to drift back to sleep and forget that the shadow could still be out there.
My first, and only, experience with sleep paralysis occurred when I was about 6 years old and coincided with my sleep-walking phase. It was a brief but terrifying experience and although I don’t remember it perfectly, the feeling of vulnerability and that shadow’s presence remain with me. The experience of sleep paralysis differs from person to person but there are constants to everyone’s experience. There is the characteristic paralysis of voluntary muscles and often, but not always, this is accompanied by hallucinations which can leave the person frightened and disoriented. The hallucinations experienced by sufferers of sleep paralysis also appear deeply embedded in different cultures, literature and history (see sleep paralysis as a cultural phenomenon below).
These hallucinations can be grouped into intruder, incubus and vestibular hallucinations. The intruder hallucination, whereby there is a feeling that there is a being in the room with you, with the feeling of malevolent intent is the type I experienced as a young child. However, experiences of a great weight on your chest attributed to a demon-like creature and the feeling of floating can be identified as incubus and vestibular hallucinations respectively. These experiences are particularly distressing for those who are unfamiliar with their cause and has led some to wrongly believe they were suffering from psychosis.
Although a bizarre experience, it is not all that uncommon. A large systematic review (a comprehensive report which gathers all of the studies, in theory, ever conducted on a topic) of the prevalence of sleep paralysis found that “7.6% of the general population, 28.3% of the student population, and 31.9% of psychiatric patients experienced at least one episode of sleep paralysis” (Sharpless & Barber, 2011). It’s interesting to note that it should be so prevalent amongst student populations.
So, what is at the root of sleep paralysis episodes? It appears that sleep paralysis is linked to REM sleep and the transition to and from this stage of the sleep cycle. Interestingly, in a sleep disorder known as narcolepsy, characterised by sudden onsets of sleep, the prevalence of sleep paralysis is around 50%. This is considerably higher than the normal population, and it might be due to the sudden onset of REM sleep seen in individuals with narcolepsy. Moreover, narcolepsy is also associated with partial sleep paralysis. This is where there is some limited movement available to the individual but they are likely paralysed and experience the powerful and frightening hallucinations seen in sleep paralysis.
In my last article, I talked about how it is possible to induce sleepwalking in those with a genetic risk by sleep depriving them. It appears that the same trick can be useful in eliciting sleep paralysis episodes in students. A study by Takeuchi and colleagues (1992) showed that by waking students up at just the right time they were able to elicit sleep paralysis in their sample. More specifically, by waking up participants when they were just about to enter REM, they were able to manipulate it so that participants were more likely to go directly into REM sleep as they drifted off again. However, this technique is far from perfect in eliciting sleep paralysis as out of 64 successful REM interruptions, only 6 episodes of sleep paralysis were recorded in 5 out of 16 participants. This suggests that sleep onset REM is involved in sleep paralysis but there are likely other factors which play a role here. For example, stress and physical tiredness (beyond being woken up in a sleep laboratory) may also contribute to the likeliness of sleep paralysis occurring. This may explain why student and psychiatric populations are more prone to sleep paralysis episodes.
As I have already, hopefully, addressed with sleepwalking, there is a clear and long history of sleep paralysis as recorded in literature and historical medical reports. We have identified the different subtypes, linked it to a particular stage of sleep and started to identify some connections with other sleep disorders (e.g. narcolepsy). However, this is largely where our understanding of the phenomenon ends. It appears that problems in the REM stage of sleep are important in the production of sleep paralysis but more work is needed to understand what these are and why they are important.
Sleep Paralysis as a Cultural Phenomenon
Sleep paralysis occurs across a wide range of different cultures and there is historical evidence of it occurring throughout the history of medicine and literature. Folk terms such as the “old hag”, the “Pandafeche”, and visitations by demonic presences such as succubi and incubi have been attributed to sleep paralysis.
Many of these lay blame for experiences on paranormal or spiritual beings, with a focus on witch or ghost-like beings (old hag and pandafeche), and given the content of hallucinations experienced alongside sleep paralysis this is not surprising.
The painting, ‘The Nightmare’ by Henry Fuseli is commonly believed to be a depiction of sleep paralysis and a case study from the 1600s exists which describes sleep paralysis in vivid detail (Kompanje, 2008). Interestingly, the previous case study also highlighted how body position while sleeping might contribute to sleep paralysis and hallucinations experienced with it. There is some recent evidence which suggests that lying in a supine position (on your back, face up) may be associated with increased rates of sleep paralysis and associated hallucinations. The 17th century case study provided the earliest evidence of this facet of sleep paralysis.
Header Image: Sleep-paralysis-pic
Additional Info Image: Demon