Have you ever been sleeping and dreamed that you were falling? Then, all of a sudden, your body jerks and wakes you up. This can feel strange or scary, but it is actually very common. This sudden movement is called a hypnic jerk. A study in 2016 found that about 60–70% of people experience it at some point.
The Stages of Sleep
Before we explain what causes hypnic jerks, it helps to understand the different stages of sleep.
Stage One
This is the stage when you first begin to fall asleep. It only lasts a few minutes. During this time, your heart rate, breathing, and eye movements slow down. Your muscles start to relax, although they may twitch from time to time. Your brain activity also begins to slow as you move from being awake into sleep.
Stage Two
This stage is a light sleep phase before deeper sleep begins. Your heartbeat and breathing become even slower, and your muscles relax more. Your body temperature also goes down, and your eyes stop moving. Your brain activity slows overall, but it still has brief bursts of activity from time to time.
Stage Three
You need Stage Three to wake up feeling rested. In this stage, your heartbeat and breathing are very slow, and your muscles are fully relaxed. It is also the deepest part of sleep, so it can be hard to wake you up.
REM Sleep
REM sleep happens about 90 minutes after you fall asleep. During this stage, your eyes move quickly side to side, and your brain becomes more active, almost like when you are awake. Your breathing gets faster and uneven, and your heart rate and blood pressure rise closer to normal waking levels. This is also the stage where most dreaming happens.
You go through these sleep stages about four or five times each night, and the length of each stage can change depending on the cycle.
Hypnic Jerks
Hypnic jerks are sudden, involuntary movements that happen when you are falling asleep. They are also called “sleep starts” or hypnagogic jerks. Scientists do not fully understand them, but they often happen more when you are very tired or forcing yourself to stay awake while your body wants to sleep.
According to sleep specialist Rafael Pelayo, this may happen because part of your nervous system is already asleep while another part is still awake.
In simple terms, a hypnic jerk is like a mistake in your body’s signals—your brain and body are not fully in sync as you fall asleep. This usually happens as you move from being awake into the first stage of sleep. Normally, you go through different sleep stages before reaching REM sleep, but when you are very sleep-deprived, your body may jump quickly into REM sleep and skip some stages.
Pelayo explains that hypnic jerks are a clear sign that your body really needs rest and sleep, and ignoring it won’t fix the tiredness.
Are Hypnic Jerks Dangerous?
Luckily, hypnic jerks are not harmful. Even though they can feel scary, they are normal and do not need treatment. Some people may feel worried afterward and have trouble falling back asleep. If that happens, it helps to remind yourself that nothing is wrong and it doesn’t mean anything serious. This can help you relax and sleep again.
Hypnic Jerks and Lack of Sleep
Sometimes, hypnic jerks can happen when you are trying to stay awake, like during a class or meeting. If this happens, sleep specialist Rafael Pelayo suggests a few tips:
- Focus on something important in the situation instead of thinking about sleep
- Try to make eye contact with the speaker to stay alert
- Drink coffee beforehand if you know you might feel sleepy
- Make sure to get 7 to 9 hours of sleep every night so you don’t become too tired
Even though hypnic jerks are not dangerous, they can be a sign that your body needs more rest. If they happen often, it may help to look at your sleep habits and make changes.