Sleep paralysis

When does sleep paralysis occur?

Sleep paralysis happens when someone is awake and conscious, but the part of the brain that controls their muscles is in 'sleep mode'. They are fully awake, but can't move. Sleep paralysis can occur when falling asleep, waking up, or both.

Sleep paralysis can last from a few seconds, up to a minute or two.

Sleep paralysis doesn't cause any physical harm. Once it wears off, people can move and speak normally. However, it can be very frightening to experience.

What happens during sleep paralysis?

During an episode of sleep paralysis, people are conscious and aware of their surroundings, but can't move or speak.

Rapid eye movement (REM) sleep normally occurs just after going to sleep and after waking, and a few times during the night. During REM sleep, the brain shuts down conscious control of muscles, causing a temporary paralysis. This is a normal part of sleep. We often dream vividly during REM sleep.

Sleep paralysis seems to happen when people are entering or leaving a REM sleep cycle, but are aware of what's happening. They have some awareness of what's happening, including being unable to move or talk.

This experience can be frightening and distressing, particularly if you don't know what's happening.

It's quite common to have hallucinations, too. People may see, hear, or feel things that are not really there. These are called hypnagogic hallucinations if they occur when falling asleep, and hypnopompic hallucinations if they occur when waking up.

Examples of hallucinations in sleep paralysis include:

• The intruder hallucination: seeing, feeling, or otherwise perceiving someone or something dangerous in the room.

• The incubus hallucination: feeling like someone or something pressing on the chest. Some people feel like they are struggling to breathe or suffocating. Sometimes people feel like someone or something is trying to have sex with them, hence the name 'incubus'.

Historically, these hallucinations have sometimes been interpreted as visits by demons or other supernatural creatures.

How long does sleep paralysis last?

An episode of sleep paralysis can last anything from a few seconds to a few minutes.

What causes sleep paralysis?

Muscles normally become relaxed and temporarily paralysed during REM sleep. Sleep paralysis occurs when some aspects of REM sleep happen whilst awake. This means that people remain temporarily paralysed but are fully conscious.

It's thought, too, that the 'emergency response' part of the brain activates during an episode of sleep paralysis. This causes people to be alert, anxious, and hyper-vigilant for any potential threats, which probably explains why the brain tends to experience hallucinations of dangerous things.

We don't know exactly why these things happen. Things that disrupt sleep might make them more likely to occur. Some things that have been linked to sleep paralysis, and might cause it, include:

• Anxiety.

• Stress.

• Sleep deprivation.

• Alcohol use.

• Having experienced a traumatic event in the past, such as abuse.

• Genetics; some studies suggest that there might be a genetic link to sleep paralysis.

• Narcolepsy.

• Disrupted sleep habits.

How common is sleep paralysis?

Sleep paralysis is common. About 1 in 10 people have at least one episode of sleep paralysis during their lifetime, although some have estimated that it might be as high as 1 in 2 people. Sleep paralysis can affect people of all ages. It's more common in students. There may be differences amongst ethnic groups; a little bit of evidence suggests sleep paralysis is more common in people of Asian, African, or Hispanic ancestry, although this isn't certain. It's also more common in people who have anxiety, panic disorder and post-traumatic stress syndrome.

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How to avoid sleep paralysis

The best way to treat sleep paralysis is to make sure you:

• Have enough sleep.

• Have regular sleep schedules and patterns.

• Are relaxed and comfortable when going to bed.

Sleep paralysis isn't physically harmful and it usually goes away on its own with time.

It's important to treat anything else that could be causing sleep paralysis, such as stress, depression, or anxiety. Cognitive behavioural therapy can be helpful in treating these.

Treatments using medicines

Your GP may refer you to a sleep clinic if your symptoms are severe or you have any other problems with sleep.

It's unusual for sleep paralysis to be severe enough to require medications. However, some people do get frequent or severe attacks of sleep paralysis.

Antidepressant medications are sometimes used by sleep specialists to treat sleep paralysis. They include:

• Tricyclic antidepressants, like imipramine, clomipramine, and amitriptyline.

• Selective serotonin reuptake inhibitors (SSRIs), like fluoxetine.

What is the outcome (prognosis)?

Sleep paralysis is harmless, although it can be distressing to experience. It doesn't cause long-term problems. Many people only experience sleep paralysis once or twice in their lifetime.

Episodes of sleep paralysis tend to become less frequent as you get older and they usually disappear. However, sometimes the sleep paralysis goes away for a time but then starts again. This can cause sleep deprivation if you aren't getting enough sleep because of it.