How many times have you been startled in your sleep and woke up scared because you didn't know where you were?

Although this experience can be quite unpleasant, you should definitely know that it is not dangerous.

That is, even 70 percent of people have experienced this phenomenon, which is called a hypnic jerk.

This jerk appears suddenly and can involve the whole body or parts of the body and you feel it like an electric shock or you have the feeling that you are falling, Dr. Ray Dasgupta explained, Telegraph reports.

Hypnosis most often occurs in the transition between wakefulness and sleep, and it is not unusual for it to occur in different stages of sleep.

It is still not entirely clear why it happens, but many scientists consider it an evolutionary sign, that is, they link it to the distant past when a man slept in a tree and a jerk during sleep would prevent him from falling.

Most often, these four things cause why the hypnic jerk occurs:

1. Insomnia

– Poor sleep quality means you don't get deep REM sleep which is restorative.

Although you spend the recommended 7 to 9 hours in bed, you probably wake up sleepless and sleepy during the day.

2. Caffeine

– Stimulants, such as caffeine and nicotine, are also related to hypnic jerks.

And it's no surprise that lack of sleep and caffeine consumption can go hand in hand.

3. Apnea

- Since hypnic jerks occur during the transition between wakefulness and sleep, they are more likely to occur if you have apnea, a condition marked by brief interruptions in breathing during the night, which causes multiple awakenings.

4. Stress

Emotional and mental stress can cause hypnic tremors.