Ever find yourself briefly paralyzed as you’re falling asleep or just waking up? It’s a phenomenon is called sleep paralysis, and it’s often accompanied by vivid sensory or perceptual experiences, which can include complex and disturbing hallucinations and intense fear.

For some people, sleep paralysis is a once-in-a-lifetime experience; for others, it can be a frequent, even nightly, phenomenon.



Hypnagogic and hypnopompic hallucinations are symptoms commonly experienced during episodes of sleep paralysis. Some scientists have proposed this condition as an explanation for reports of alien abductions and ghostly encounters. A study by Susan Blackmore and Marcus Cox (the Blackmore-Cox study) of the University of the West of England supports the suggestion that reports of alien abductions are related to sleep paralysis rather than to temporal lobe lability. There are three main types of these hallucinations that can be linked to pathologic neurophysiology. These include the belief that there is an intruder in the room, the incubus, and vestibular motor sensations

Researchers James Allan Cheyne and Gordon Pennycook of the University of Waterloo in Canada explore the factors associated with distress after sleep paralysis episodes in a new article published in Clinical Psychological Science, a journal of the Association for Psychological Science.

The Nightmare, by Henry Fuseli (1781) is thought to be one of the classic depictions of sleep paralysis perceived as a demonic visitation.

Credit: Wikipedia The researchers used an online survey and follow-up emails to survey 293 people. They measured post-episode distress using a range of items, from post-episode rumination to interference with next-day functioning. The level of distress following sleep paralysis episodes was associated with features of the sleep paralysis episode itself. For example, the results showed that the more fear people felt during sleep paralysis episodes, the more distress they felt afterward. The researchers also found that sensory experiences during episodes of sleep paralysis predicted later distress. Feelings of threat and assault — such as sensing a presence in the room, feeling pressure on the chest, having difficulty breathing, or having a feeling of imminent death — were all associated with distress following sleep paralysis episodes. So, too, were vestibular-motor experiences, including feelings of floating or falling and out-of-body experiences. Cheyne and Pennycook speculate that the sensory experiences that come with episodes of sleep paralysis could exacerbate people’s fear, creating a feedback loop that enhances memories of experiences later on. Post-episode distress was also associated with a number of individual-level factors, including cognitive style, distress sensitivity, and supernatural beliefs about sleep paralysis. People who held supernatural beliefs about sleep paralysis experiences also experienced greater post-episode distress. Those who had more analytic cognitive styles, on the other hand, experienced comparatively less distress after sleep paralysis episodes. Taken together, these findings show that both situational factors and individual factors contribute to these common, and often stressful, personal experiences. These findings are important, the researchers say, because they provide insight into a common experience of distress that is not well understood. Some participants lamented that their experiences of terror following episodes of sleep paralysis were often dismissed by clinicians. Given that a large percentage of people report some carryover effects on their functioning the next day, sleep paralysis could “make a significant contribution to the billions of dollars, worldwide, in costs associated with accidents, illnesses, and lost productivity associated with sleep disturbances,” the researchers note.

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