Exhausted, you crawl into bed, drifting toward sleep when suddenly, you feel as if you’re falling—your body jerks involuntarily, jolting you awake. This common phenomenon, known as a hypnic jerk or sleep start, affects up to 70% of people.

One theory suggests that as muscles relax, the brain misinterprets it as falling, triggering a sudden neural response to “catch” the body. Another theory links it to the nervous system struggling to transition smoothly from wakefulness to sleep.

Stress, anxiety, and fatigue may increase the likelihood of hypnic jerks, as an overactive nervous system remains on high alert. While generally harmless, they can be frustrating when disrupting sleep. Recognizing them as a normal part of the sleep process may help ease any concerns.