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 hypnic jerks. It can be confusing because it’s also sometimes referred to by 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 – this is the medical term to describe an involuntary muscle twitch.
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, during what’s known scientifically as the hypnagogic state of consciousness.
That’s why they’re sometimes call hypnagogic jerks: 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 various possible expressions to describe the same thing.
When you experience a hypnic jerk it often causes you to wake up suddenly. And when you wake up you may feel like you’re experiencing a sudden and dramatic falling or jolting sensation.
Interestingly, 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 the phase of falling asleep that several unusual phenomenon may take place. For example, I discussed in a previous article the various sleep paralysis experiences people have. Those often come with bizarre or frightening hallucinations and even out-of-body experiences.
Luckily there’s nothing to be worried about – hypnic jerks along with these other phenomenon aren’t dangerous. They may be unsettling or annoying, but you don’t need to fear going to sleep just because they may happen to you.
What causes the hypnic jerk?
So now you know that the hypnic jerk is a twitching of the muscles. But what causes the muscles to twitch in the first place?
As is often the case in the complex world of sleep, scientists still aren’t 100% certain about the cause. However, they do believe that the following factors can all contribute to hypnic jerks happening:
- Heavy exercise late in the evening.
- Sleeping in an uncomfortable position.
- Being very tired or fatigued.
In addition to these factors which can contribute to the likelihood of a hypnic jerk occurring, there are some theories as to why they happen:
- The first theory is that they happen as your nervous system relaxes and slows down when transitioning from wakefulness to sleep. Your breathing slows down, temperature drops and your muscles relax. So they might happen when nerves misfire during this slowing down process, resulting in the muscular spasm.
- The second theory is that while relaxing as you fall asleep, your brain sometimes gets confused and thinks you’re falling. So it sends signals to the arms and legs to move to an upright position, resulting in the jerking sensation.
- Following from the second idea, a popular evolutionary theory suggests that the ancient primate brain may have mistaken relaxation for falling out of a tree, and so the jerking is the brain waking you up quickly to take action.
- Another evolutionary theory suggest that your brain wakes you up one last time so you can check that you’ve take the necessary steps to keep yourself safe at night.
For the majority of people though, the hypnic jerk is a common and harmless phenomenon.
How can you stop hypnic jerks?
The hypnic jerk is such a common occurrence that it may not be possible to prevent it happening completely. However, you can take steps to address some of the factors thought to increase the likelihood:
- Cut down on alcohol and caffeine, especially in the 3-4 hours before going to bed.
- Try not to do heavy exercise late in the evening or night.
- Ensure you’re getting sufficient magnesium and calcium in your diet – this can help with muscle and nerve spasms.
- Make sure you have a comfortable mattress and bedding, and that you sleep in a comfortable position, even with a partner.
- Try not to allow yourself to get too tired or fatigued.
Avoid the vicious cycle of worry
Hypnic jerks can become cyclical if you start worrying about them. This is a very common thing that happens with many sleeping difficulties.
For example, people who have insomnia will often start worrying that they won’t be able to get to sleep. This worrying then becomes the thing that causes their insomnia, even if the original cause has long gone.
So in the same way if you worry about hypnic jerks you may start to get less sleep and become more fatigued. Being fatigued is thought to contribute to the frequency of hypnic jerks, and so it’s more likely you’ll experience them.
You now know that hypnic jerks aren’t dangerous and that many people experience them. So hopefully you can start to relax about them and not go to bed thinking about them.