If you’re unsure if you’ve ever experienced a hypnic jerk, then ask yourself this question:
Have you ever woken up with a sudden jolt just as you’ve started falling asleep? Or maybe it felt like you were falling?
It could be that it felt like you were having a huge muscle spasm. You may have even felt a small shock sensation or a bouncing feeling.
Perhaps it was even your partner that was experiencing it, and this in itself startled you back to consciousness.
It could be then (though not necessarily) that you experienced a hypnic jerk. And if so, you’re certainly not alone.
It’s estimated that around 70% of people experience hypnic jerks at some point in their lives. I know I definitely have.
The world of sleep can be confusing, and there’s no exception when it comes to the hypnic jerk. Confusing because it’s also sometimes called by one of the following names:
- Night starts.
- Sleep starts.
- Hypnagogic jerk – hypnagogic being a term used to describe the period of time when falling asleep.
- Myoclonus, or myoclonic jerk – technically this is the medical term to describe an involuntary muscle twitch.
So what is a hypnic jerk exactly?
A hypnic jerk is an involuntary twitching of a muscle, or muscles (the myoclonus as mentioned above). They usually occur just as you’re falling asleep. This is referred to scientifically as the hypnagogic state of consciousness.
This is why they are sometimes call hypnagogic jerks – because you most commonly experience them when falling asleep.
Note that hypnic is also a shortened version of the word ‘hypnagogic’. So you can see why there are all these possible expressions to describe the same thing.
When you experience a hypnic jerk it often causes you to wake up suddenly. When you wake up you may feel like you’re experiencing the sensation of falling or jolting.
Note that the muscle twitching you experience also occurs in other situations. For example hiccups are also muscle twitches.
That strange time of the night
It’s during this phase of falling asleep that several unusual phenomenon may take place. For example we discussed in a previous article the various sleep paralysis experiences people have. Those often come with bizarre or frightening hallucinations, or even out-of-body experiences.
Luckily there’s nothing to be worried about – hypnic jerks along with these other phenomenon are not dangerous. They may be unsettling or frightening, but you don’t need to fear going to sleep just because they may happen to you.
Another popular idea takes a more evolutionary approach to hypnic jerks, explaining that the spasms are an ancient primate reflex to the relaxation of muscles during the onset of sleep — the brain essentially misinterprets the relaxation as a sign that the sleeping primate is falling out of a tree, and causes the muscles to quickly react.