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. If you’ve experienced it, you’re certainly not alone—up to 70% of people report having this strange jolt as they fall asleep. Despite being so common, it never seems any less abrupt or surprising when it happens.
But why does this happen? What exactly is going on inside the body that causes such an involuntary and sometimes violent jerk right as you’re drifting off to sleep? While the exact cause remains somewhat of a mystery, there are a few widely accepted theories about what might be triggering these sudden movements.