Why is it, that when you’re all tucked up in bed at night and you’re just about to drift off, your body decides to wake you up with an involuntary jolt? It’s that strange jumping-in-your-sleep feeling which leaves you feeling puzzled and less relaxed than before.

Read on to discover why it happens, what causes it and how to avoid it.

What is a hypnic jerk?

A hypnic jerk – also known as a sleep or night ‘start’ – is an involuntary muscle spasm than happens in your arms, legs or whole body, just as you are drifting off to sleep.

If you’ve felt this strange sensation – like a jump or a fall in sleep – you’re not alone as it’s a very common occurrence in adults and children. It is said that up to 70% of people experience them occasionally.

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What causes hypnic jerks?

So, what causes those crazy muscle twitches?  They can be induced by sound and light or other external factors. Scientists don’t have a definitive answer but the following are known as potential causes for hypnic jerks:

  • Alcohol
  • Caffeine
  • Stress
  • Extreme tiredness
  • An uncomfortable position for sleep

There are a few theories for why these jerks happen. One is that as you relax because you are drifting off to sleep, your brain becomes confused and presumes you are falling. This in turn, sends a message to your legs to move to a standing position, resulting in a jolt.

Exercising too close to bed time can cause your muscles to become tense, which is said to be another reason for these jerks.

Another theory is that because your body is shutting down into sleep mode, your breathing and heart rate both slow down and your body temperature drops, resulting in these twitches as your muscle tone changes.

Is hypnic jerking dangerous?

The action itself is not dangerous but consistently worrying about it happening, could bring about anxiety in a person. Side effects of sleep deprivation can be bad for your health if it happens over a long period of time.

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How can I avoid jumping in my sleep?

Follow these tips to try to prevent hypnic jerks:

  • Go to bed earlier where possible, to avoid being over-tired.
  • Avoid drinking alcohol or caffeine at least four hours before you plan to go to bed.
  • Taking a calcium or magnesium supplement can help with nerve spasms.
  • Try some relaxation exercises before bed, such as yoga or pilates.
  • A warm shower before bed can help relax muscles.
  • Ensure you have a firm mattress and that you fall asleep in position that is comfortable.


Hopefully now you know a bit more about hypnic jerks – what causes them and how to prevent them, but if the problems persist, you could seek advice from a sleep therapist.