HealthTalk: Sleep paralysis

“The Nightmare,” by John Henry Fuselli, captures the heaviness on the chest and strange imagery evoked by sleep paralysis. (credit: Courtesy of Wikimedia Commons) “The Nightmare,” by John Henry Fuselli, captures the heaviness on the chest and strange imagery evoked by sleep paralysis. (credit: Courtesy of Wikimedia Commons)

Nighttime can be unsettling: We hear noises that we cannot immediately recognize, and the most we can see might be the numbers on our alarm clock. But imagine waking up with a tremendous pressure across your chest — making it impossible to breathe — and seeing a black cat with a white inverted skull hissing next to your bed. And imagine being unable to move.

This terrifying experience was documented by Chris French, a professor of psychology at Goldsmiths College, of the University of London, who suffers from sleep paralysis. Sleep paralysis is a phenomenon that occurs when our mind remains aware as we start to dream.

Sleep can be broken down into at least five different stages. One of the most well-known stages is called REM sleep, which is when we have vivid dreams. REM stands for “rapid eye movement”; when a person is in this stage of sleep, his or her eyes dart around quickly even while they are closed. REM sleep lasts around 90 minutes, according to

During REM sleep, a person’s heart rate and breathing become irregular, blood flow changes, and regulation of the body temperature diminishes. In addition, the activity of certain neurotransmitters can be inhibited. Neurotransmitters are chemicals responsible for almost all actions of the body, including emotions, movement, and thought. During REM sleep, any motor activity that our brain monitors is inhibited and the activity of our muscles decreases to the point of paralysis. This phenomenon is called REM atonia, and it is responsible for the feeling of paralysis. If this were not the case, we would act out the motions of our dreams, a condition which has also been documented as a sleep disorder.

We fall asleep, or drift out of consciousness, slower than our brains can induce REM sleep, so it is normal for us to dream before we are fully asleep. However, this timing can sometimes be too far off, causing sleep paralysis. As a result, REM atonia can occur before a person is fully asleep, or while he or she is still aware. This is called hypnagogic, or predormital, sleep paralysis. Conversely, when a person wakes up before REM atonia is complete, hypnopompic, or postdormital, sleep paralysis may occur.

Sleep paralysis is an unsettling experience because a person is dreaming while awake. Many people have had dreams in which they lost the ability to run or move away from an unpleasant image; people experiencing sleep paralysis have lost this ability while completely conscious. According to a presentation by Susan J. Blackmore, a psychologist at the University of West England, a person might experience a sensation of floating and hear buzzing and humming noises. They may also feel intense fear and pressure on the chest. Hearing screams, laughter, and one’s name being called have also been reported.

These strange experiences can be explained by changes in brain activity during sleep. According to Ian Newby-Clark, a professor of psychology at the University of Guelph, when scientists studied sleep paralysis, they found that the area of the brain that becomes active when a threat is present is activated; therefore, people feel fear towards an entity that does not really exist. In addition, the muscles in our chest that make us feel like we can breathe are inactivated, so we feel as if something heavy is pushing down upon us. Scientists have attributed some sounds to muscle spasms in the middle ear, which is a part of the ear responsible for creating auditory signals that are eventually sent to the brain. Other sounds can be explained by interpreting actual sounds incorrectly, such as a ticking clock that may be heard in a dream as footsteps.

Some researchers have used sleep paralysis as an explanation of alien abductions or ghost sightings, since hallucinations of lights or moving shadows are common, as are feelings of movement and hearing the sound of a motor.

The biology of sleep is still mysterious, and that of sleep paralysis even more so. Still, there are a few methods a sufferer of sleep paralysis can try to reduce the frequency of its occurrence. Regular sleep patterns and a healthy amount of sleep have been shown to decrease instances of sleep paralysis. Irregular sleep patterns causes disruption of REM sleep, which can increase the chance of sleep paralysis occurring. In addition, a correlation between sleeping on one’s back and sleep paralysis was found. Substance abuse, such as drinking large amounts of alcohol before sleeping, can also induce sleep paralysis.

While sleep paralysis can be frightening, all of the dangers are truly in one’s mind, and it is a physically harmless experience.