Exhausted, you finally crawl into bed, eager for a good night’s sleep. Your body sinks into the mattress, and your mind starts to drift into that soothing space between wakefulness and sleep. But just as you’re about to fully surrender to slumber, a sudden sensation hits—it’s as if you’re falling through the air, plummeting down with nothing to hold onto.

In a split second, your body jerks involuntarily, startling you wide awake.

This sudden and often unsettling movement is known as a hypnic jerk, also called a sleep start.