Sleep paralysis: what it is, why it happens and how to get out of it

What is sleep paralysis?

In an episode of sleep paralysis you know you're in your bed, you can see the room or think you can, but you can't move your arms, your legs or your mouth. You try to scream and nothing comes out. It often comes with intense fear, and sometimes with the feeling that someone else is in the room.

It happens on the border between sleep and waking: as you drift off or, more often, as you wake up. It's usually brief. According to a clinical review by the psychologist Brian Sharpless, episodes last from a few seconds to about twenty minutes, around six on average. From the inside, though, it feels much longer.

What happens in your body: REM atonia

Sleep paralysis comes from a normal part of sleep. During REM sleep, the stage of the most vivid dreams, the brain relaxes nearly all your voluntary muscles. That atonia is a safeguard: it keeps you from acting out your dreams, running or swinging your fists while you dream you're fleeing or fighting.

In an episode, part of the brain wakes up before the atonia has worn off. Awareness comes back, but the muscles don't respond yet. That's why you can move your eyes and keep breathing: the eyes and the diaphragm don't switch off in REM sleep. What you can't do, for a few moments, is move the rest of your body.

Because the brain is still halfway between dreaming and waking, the images and sounds of the dream can blend into the real room. That's where the hallucinations come from, the part that makes the experience so unsettling.

The presence in the room and the weight on your chest

Many people sense a presence during sleep paralysis: someone by the bed, in the doorway or in a corner, almost always menacing. Some see a shadow or a figure; others hear footsteps, voices or buzzing. Another very common sensation is a weight on the chest, as if something or someone were crushing you and breathing were hard.

The Canadian psychologist J. Allan Cheyne and his colleagues studied many accounts like these and, in 1999, proposed sorting them into two families. The intruder group gathers the presence, the fear and what is seen or heard; the authors tied it to a hypervigilant state in which the brain searches for a threat and gives it a shape. The incubus group gathers the chest pressure and the struggle for air, which they linked to how breathing feels when the muscles are relaxed. Later work by Cheyne also described sensations of floating or leaving the body.

Knowing this doesn't take away the fright in the moment, but it helps a great deal afterward: what you saw or felt is a known way of dreaming with your eyes open, not a visit.

How common is sleep paralysis?

Sleep paralysis is far more common than most people think. In 2011, Brian Sharpless and Jacques Barber pooled 35 studies covering more than 36,000 people and estimated that about 7.6% of the general population has had it at least once. The figure climbs to about 28% among students and nearly 32% among psychiatric patients.

Some things make it more likely: too little sleep, irregular hours or shift work, sleeping on your back, stress, and conditions such as insomnia, anxiety or PTSD. It can also run in families.

What cultures call it

Sleep paralysis shows up in the stories of many cultures, each with its own name and its own explanation. Here are some of the best known:

• The old hag: in Newfoundland, tradition held that a hag sat on the chest of the sleeper. The folklorist David Hufford studied it in his book The Terror That Comes in the Night (1982) and found that people who had never heard of the old hag described the very same experience.
• "Se me subió el muerto", "the dead climbed on top of me": that's what people say in Mexico. A study of teenagers in Mexico City, published in 2009 by Alejandro Jiménez-Genchi and colleagues, started from that popular phrase and found it described the same experience doctors call sleep paralysis.
• Kanashibari: in Japan, this word evokes being bound or held fast. In a 1987 survey of 635 college students, Kazuhiko Fukuda and his team found that about 40% had experienced it at least once.

Sleep paralysis is harmless

Sleep paralysis is frightening, but it doesn't hurt you. The UK's National Health Service (NHS) describes it as harmless, and for many people it happens only once in their lives. It doesn't cut off your air: even if your chest feels crushed, your diaphragm keeps working and you breathe throughout. It always ends on its own, and you can't get stuck in it.

It isn't a possession, an omen or a warning either. Folk traditions explained it with spirits, and those stories are worth understanding, but what's happening in your body is a timing mix-up between sleep and waking.

How to get out of a sleep paralysis episode

There's no proven technique for ending an episode on the spot, but there are things many people find helpful. In 2016 the neuroscientist Baland Jalal proposed an approach that combines meditation and relaxation, and that runs against the urge to fight:

• Tell yourself: "This is sleep paralysis. It's common, it's not dangerous, and it will pass."
• Remind yourself there's no reason to be afraid. Fear tends to intensify the hallucinations and stretch out the experience.
• Bring your attention to something that calms you: a cherished memory, a prayer, the face of someone you love. If your attention slips, bring it back.
• Let your muscles go slack instead of straining against them, and let your breathing carry on by itself, without forcing it.
• Other people say it helps to focus on moving something small, like a finger or your eyes, until the body responds, although Jalal advises against trying to move. Calmly find what works for you.
• When it's over, sit up, turn on a light and breathe for a moment before going back to sleep.

How to make it less likely

Sleep paralysis shows up more when sleep is out of order, so looking after your sleep is the best prevention. The NHS suggests getting seven to nine hours, keeping regular times for going to bed and getting up, exercising but not right before bed, avoiding big meals, alcohol, smoking and caffeine close to bedtime, and not sleeping on your back, since that position makes episodes more likely.

When to see a doctor

A single episode doesn't call for a visit. It's a good idea to see a doctor if episodes happen often, if they make you afraid to go to sleep, or if poor sleep leaves you tired all day. Sometimes another treatable problem is behind it, such as insomnia or PTSD.

Sleep paralysis can also be one of the symptoms of narcolepsy, an uncommon sleep disorder. Talk to a doctor, who can refer you to a sleep clinic, if you also notice any of these signs:

• Strong sleepiness during the day, even when you sleep enough.
• Falling asleep suddenly, without meaning to, for example mid-conversation or while eating.
• Sudden muscle weakness when you laugh, get angry or feel a strong emotion: your knees buckle, your head drops or your speech slurs. This is called cataplexy.
• Very vivid dreams as you fall asleep, or waking up often during the night.