Drained and exhausted, you are finally in bed sinking into what will be a deep sleep, when your body starts ‘falling’ and it suddenly jerks to stop that ‘fall’. You will of course wake up immediately and wonder where it came from.

And no matter how many times happens, you never get used to it, it never feels less abrupt, and it never gets any better. The falling sensation can even be terrifying, which ends with an involuntary, sudden, and shocking jump.

If this has happened to you at least once, you are not alone. In fact, up to 70% of people experience this phenomenon, also known as hypnic jerks (or sleep starts). Nobody really knows what causes these sudden jerks for sure.

The  science behind hypnic jerks

Although a solid explanation for how and why hypnic jerks happen hasn’t been offered, there are two theories that suggest some reasons for this. One states that the hypnic jerks happen as a result of the natural downshifting of the nervous system as you’re falling asleep.

It owes its explanation to the shifts of the muscle tone, which happen as a result of the slowing down of your breathing and heart rate, and the natural drop of your body temperature. In this transition, the theory suggests that the twitches come as a response to this downshifting.

The other theory suggests that it happens as a result of the rapid relaxation of your muscles, which your brain interprets as if you are actually falling. In response, it signals the muscles to tense up, so that you could protect yourself.

Whatever the case, researchers think that this response of the body comes under the influence of external factors, such as caffeine, tobacco, sleep deprivation, and it’s even associated with the intake of medications like Adderall and Ritalin, which can have similar effects.

Is it normal to have hypnic jerks every night?

These jerks are sudden and involuntary, which means you have no control over them. Some people may feel startled and some may feel falling. But whatever the case, it is considered to be absolutely normal to experience hypnic jerks during sleep. “It’s a kind of signal to the body that is going into sleep mode. It’s not a disorder. In fact, it is a natural phenomenon,” says Dr Rustgi.