Why Hypnic Jerks Happen

Have you ever had this happen to you? When you are sleeping soundly, you suddenly feel

like you have fallen from a height and you are startled. This is called a hypnic jerk in science.

This is not a nightmare, but an overreaction of your brain. When we fall asleep, our heartbeat slows

down and our muscles relax. Then your brain gets confused and thinks,

"Hey, is this person dying?" and gives you an electric shock to alert you.

That's the jerk. That is, your brain's attempt to save you. So next time If

this happens, don't panic and go back to sleep.