You're almost asleep when your whole body jolts, like you missed a step. Out of 100 people, how many get that jolt?

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Up to 70% of people get sleep starts, the medical name for hypnic jerks. Nobody is certain why it happens. The leading explanation is that as the brainstem hands control over to sleep, that handover is unstable and sends a sudden burst of signals down to the muscles. Another explanation is that the brain reads your muscles going slack as falling, and jerks you awake to catch yourself.

That whole-body jolt as you drift off is a hypnic jerk. 70% of people get them, and most never remember.

Source: Cleveland Clinic; American Academy of Sleep Medicine · checked Jul 2020