Here’s why it happens:

1. Muscle Relaxation and Brain Misinterpretation:
As your body relaxes and your muscles begin to loosen up when you drift off to sleep, your brain might misinterpret the sensation of relaxation as a signal that you’re actually falling or losing control of your body. This causes a sudden, involuntary muscle contraction—a hypnic jerk.
Essentially, your brain can confuse the muscle relaxation with the feeling of falling, leading to the sudden “jerk” or twitch you experience.
2. Evolutionary Theory:
Some researchers believe hypnic jerks could have an evolutionary basis. The theory suggests that these jerks could have evolved as a protective mechanism. In ancient times, as people relaxed into sleep, the sensation of falling could have been a warning signal to the brain to prevent them from potentially falling out of trees or from a high place during sleep.
3. Sleep Cycle and Brain Activity:
During the early stages of sleep (Stage 1), the brain activity slows down as you drift off, and your muscles begin to relax. This can sometimes cause the body to briefly “wake up” or react as though it’s in danger, which leads to the feeling of falling or even the sensation of jerking awake suddenly.
4. Stress and Anxiety:
Stress or anxiety can also contribute to more frequent hypnic jerks. When you’re under stress, your nervous system can be more on edge, leading to more pronounced and frequent jerks as you fall asleep.
5. Sleep Deprivation or Fatigue:
People who are sleep-deprived or extremely fatigued may experience more hypnic jerks. Your body is trying to adjust quickly to falling asleep, and the process can become more erratic.
6. Caffeine or Stimulants:
Consuming caffeine or other stimulants too close to bedtime can also increase the likelihood of experiencing these jerks, as they interfere with the natural sleep transition process.
In general, hypnic jerks are completely normal and not typically a cause for concern. They can happen to anyone and are usually harmless. However, if they start interfering with your sleep or are accompanied by other unusual symptoms, it may be a good idea to speak with a healthcare provider to rule out underlying issues.