Why You Suddenly Wake Up With a Jerk During Sleep

LONDON: (Web Desk) – Many people have had a strange experience: just as they are about to fall asleep, their body suddenly jerks and their eyes open. After waking up, they often wonder what caused it.

In medical terms, this is called a hypnic jerk. During this moment, a person may briefly feel fully awake or even sit up, but sleep usually returns quickly.

Doctors explain that during sleep, the brain releases chemicals that temporarily “switch off” the muscles. This is why we do not move while dreaming, even though the brain remains active.

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Our body works through two systems, one keeps us alert and controls basic functions like breathing, while the other prepares us for sleep. When we are falling asleep, the brain shifts between wakefulness and drowsiness. Sometimes this transition is not smooth, and the brain sends sudden signals to the muscles, causing a jerk.

A popular belief says this reaction may come from human evolution. Early humans often slept in trees, and if their muscles relaxed too much, they could fall. The sudden twitch may have been a natural warning response to wake them.

Health experts say hypnic jerks are normal and harmless. However, stress, anxiety, fatigue and irregular sleep can make them happen more often. If they repeatedly disturb sleep or cause worry, doctors advise consulting a physician.