#27: The Mystery of the Hypnic Jerk
Everyone has experienced that sudden jolt while falling asleep — the feeling that you’re tripping, slipping, or falling into a hole. This involuntary muscle spasm is known as a “hypnic jerk,” and scientists have several theories behind it.
One theory suggests it comes from our primate ancestors, whose bodies would jerk awake to prevent them from falling out of trees. Another theory connects it to stress, caffeine, and overstimulation. Whatever the cause, it’s a universal experience that snaps us awake in the most confusing way possible.
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