Why does my body twitch just as I am falling asleep?

A hypnic jerk is an involuntary muscle contraction that happens when we are in between wakefulness and sleep.

Nick Beare 4 minute read April 8, 2022
Sleeping beauty floating in air. Relaxed girl in vintage ruffle dress keeping eye closed, lying on pillow levitating

Sleep spasms happen during the hypnagogic state — the period of transition between wakefulness and sleep. GETTY

Has this ever happened to you?

You’re drifting off to sleep — warm and cosy under the covers. Maybe you’re starting to dream about your next vacation, plans for the weekend, or maybe your morning coffee, when suddenly, your entire body jerks violently, waking you up — just as you were about to settle into dreamland.

What is a hypnic jerk?

A hypnic jerk, sometimes called a sleep start, myoclonic jerk or night start is an involuntary muscle contraction that is named for the hypnagogic state — the period of transition between wakefulness and sleep.

According to the Sleep Foundation, hypnic jerks occur at random, usually affect one side of your body and can happen just once or multiple times in a row.

Hypnic jerks are a type of myoclonus — or quick — involuntary muscle jerk. Hiccups, and spasms relating to anxiety or exercise are other common forms of myoclonus.

Why do hypnic jerks happen?

While we don’t know for sure why hypnic jerks occur, there are a couple theories.

According to BBC Future, hypnic jerks may indicate that the motor system has control over the body, even as sleep sets in. “Rather than having a single ‘sleep-wake’ switch in the brain for controlling our sleep … we have two opposing systems balanced against each other that go through a daily dance, where each has to wrest control from the other,” wrote author Tom Stafford.

Stress, fatigue and caffeine increase chance of hypnic jerks

According to Live Science, some scientists believe stress, anxiety, fatigue, caffeine, and sleep deprivation can increase the severity or likelihood of hypnic jerks occurring. Another theory is that intense exercise or physical activity in the evening may also cause them. And though these odds jerks often happen spontaneously, they can also be caused by sound, light, or some other stimuli around us.

And while sometimes they can be powerful enough to wake you up completely, hypnic jerks can also occur without the person noticing anything happened at all.

Who is most likely to experience hypnic jerks?

They can happen to anyone, at any time, but are more common in children, according to BBC Future. Some research suggests that about 60 to 70 per cent of people experience hypnic jerks.

Should you worry about hypnic jerks?

While some people may experience painful of tingly sensation when the jerking motion occurs, generally there should not be any pain — though you may be startled out of a fun dream.

If they happen once in a awhile, hypnic jerks aren’t usually concerning. However, if you notice they are persistent and frequent it may be worth mentioning to your doctor.

Can you prevent hypnic jerks?

If the theories about the causes of hypnic jerks are correct, avoiding rigorous exercise or coffee right before bed is probably a good idea.

Practising proper sleep habits can also help, such as going to bed and waking at the same time every day, sleeping in a dark and quiet room, not using your phone, TV or other devices close to sleep time, and making sure the temperature of the room is comfortable.

Nicotine and alcohol are other known sleep disruptors, as is a sedentary lifestyle and stress. Limiting these things as much as possible can lead to a better sleep, and in turn a lesser chance of experiencing hypnic jerks.

Hypnic jerks are just one type of myoclonus

While hypnic jerks are mostly a harmless, painless form of myoclonus, other types may occur as a symptom of a more serious condition, including an epileptic disorder, head injury, a medication reaction, Alzheimer’s disease and stroke.

Nick Beare is a Toronto-based writer.

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