What Causes Sleep Paralysis?

Medically reviewed by Alexis Appelstein, DO

Sleep paralysis is a phenomenon that causes temporary immobility while you are falling asleep or waking up from sleep. You are awake and fully alert, but your body is unable to move or speak. This happens because the part of your brain that reduces muscle movements during sleep doesn’t wake up along with the rest of your brain; instead, it remains turned off, and you feel temporarily paralyzed.

Some people who experience sleep paralysis report experiencing visual hallucinations at the same time, such as seeing someone who isn’t there. Some also report experiencing the Incubus phenomenon, which is a feeling of pressure on the thorax, or chest. Though sleep paralysis isn’t physically harmful, these occurrences combined with the temporary inability to move can be frightening.

Unlike many other sleep disorders, sleep paralysis usually doesn’t happen often: you might experience sleep paralysis just a few times per year, or even only once or twice in your lifetime. Sleep paralysis can occur due to a variety of factors, including lack of sleep or poor sleep habits, as well as by sleep-related conditions and other health conditions. Here is what you need to know about the causes of sleep paralysis.

Poor Sleep Habits and Sleep Deprivation

Not sleeping well or sleeping enough can cause sleep paralysis, especially if your lack of sleep is chronic, or ongoing. In fact, sleep deprivation is the most common reason why people have sleep paralysis.

Poor sleep doesn’t have just one definition, but some studies suggest that people who describe their sleep quality as “poor” are also more likely to report sleep paralysis. In one 2018 study, for example, “poor sleep” was defined as the combination of taking a long time to fall asleep (i.e. more than 30 minutes) and experiencing negative effects on daily life because of tiredness.

Shift workers, or people who sleep during the day and work during the night, are also vulnerable to having episodes of sleep paralysis due to poor sleep quality.

Sleep Disorders

Sleep paralysis may also be more common in people with certain sleep disorders.

Insomnia

Some studies have shown that people with insomnia—a sleep disorder that makes it difficult for people to fall asleep, stay asleep, or get restful sleep regularly—also report more frequent episodes of sleep paralysis.

Although, you don’t necessarily have to be diagnosed with insomnia to be at a higher risk. A 2018 study found that people who reported experiencing symptoms of insomnia were also more likely to experience sleep paralysis.

Obstructive Sleep Apnea

You could also be at a higher risk for sleep paralysis if you have obstructive sleep apnea (OSA), a condition that temporarily interrupts your breathing while you sleep. Because people with sleep apnea often sleep poorly and may experience several wakings per night, their risk for sleep paralysis is higher than people without sleep apnea.

Narcolepsy

Sleep paralysis can occur due to a rare neurological sleep disorder called narcolepsy. In narcolepsy, your brain can’t control your circadian rhythm (your natural sleep-wake cycle) correctly, so you often feel excessively sleepy during the day. You may fall asleep suddenly during daily tasks and have episodes of muscle weakness, or cataplexy. Many people with narcolepsy also have difficulty sleeping restfully at night.

Sleep paralysis is a known symptom of narcolepsy. This is because sleep paralysis is very similar to the loss of muscle control that happens to people who have narcolepsy with cataplexy, except it occurs as you are falling asleep or waking up from sleep instead of during the day.

Mental Health Conditions

Mental stress has been linked to an increased risk of sleep paralysis. This can be occasional stress, like the kind caused by events such as a death in the family or loss of employment, or more chronic stress. For example, post-traumatic stress disorder (PTSD) is frequently associated with sleep paralysis. PTSD is a psychiatric condition that can occur after a person experiences or witnesses something traumatic, like a serious car accident, active combat, or domestic abuse.

People with certain mental health conditions are also more likely to have sleep paralysis. In particular, generalized anxiety disorder, panic disorder, and bipolar disorder have been linked to sleep paralysis.

Is Sleep Paralysis Hereditary?

A family history of sleep paralysis makes you more likely to experience it yourself. A 2015 study among twins found there to be a possible genetic connection related to a gene called PER2 (a gene that helps regulate your circadian rhythm), noting that this gene variation had a “moderate influence” on sleep paralysis.

But there is much we don’t know about how sleep paralysis is or isn’t passed down through family members—only that you are somewhat more likely to have it if someone else in your family does, too.

Who Gets Sleep Paralysis?

Some people are more likely to experience sleep paralysis than others.

• Age: Sleep paralysis often happens for the first time in childhood or adolescence. Experiencing it as a child or teenager could make you more likely to continue having it as you get older.

• Sex: Some studies suggest that people assigned female at birth have a slightly higher rate of sleep paralysis than people assigned male at birth.

• Ethnicity: Rates of sleep paralysis are higher in people of Asian or African descent—especially those who are college students or are currently receiving psychiatric care—and lower in white people.

Risk Factors

In addition to the known causes of sleep paralysis, other things could possibly increase your risk of experiencing this disruption to your sleep cycle.

Substance Use

More research is needed to determine whether smoking, drinking alcohol, or using other types of substances increases your chances of having sleep paralysis.  A 2018 analysis of 42 studies showed that people who drank at least one alcoholic beverage or smoked at least one cigarette per day were more likely to report having sleep paralysis, but some other studies haven’t found those same results.

However, experts do know that using addictive substances (like alcohol and cannabis) regularly disrupts your normal sleep cycle, which could increase your risk of experiencing sleep paralysis.

Some Medications

Medications commonly prescribed for mental health conditions like anxiety and depression can cause your normal sleep/wake cycle to function differently, resulting in sleep paralysis. Antidepressant medications, like Zoloft (sertraline), have been associated with a higher risk of sleep paralysis, and medications for attention-deficit hyperactivity disorder (ADHD) may have a similar effect.

How You Sleep

Sleep paralysis is more common in people who sleep on their backs, possibly because of the connection to obstructive sleep apnea. Sleeping irregular hours, drinking alcohol or caffeine in the evening, and regular travel between different time zones can also disrupt your sleep schedule, thereby increasing your risk.

Related: Sleep Regularity More Important than Sleep Duration, Study Finds

A Quick Review

Sleep paralysis happens to many people from time to time, but it can also be a chronic sleep disorder. It’s not physically harmful, though it’s often frightening. Some other health conditions, like narcolepsy and sleep apnea, can cause sleep paralysis, but the most common reason is poor sleep quality. The use of certain substances and medications can also increase your risk.

If you’re experiencing frequent episodes of sleep paralysis, talk to your healthcare provider; sleep paralysis may be a symptom of another health condition. Sometimes all that is needed is to make some lifestyle changes to help yourself sleep better at night.  

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