For the most part, going to sleep is an easy thing–like falling off a log. Sometimes though, the process takes an unusual turn. Perhaps you’ve found yourself drifting off and having a dream-like vision of, say, falling off a log, upon which you’re jolted awake at the moment of impact. You’ve just been through one of the many mysteries of the human sleep experience: the hypnic jerk.
I know it sounds like a dance from the 80s, but it’s an actual thing. And isn’t nice to have a name associated with those bizarre experiences? While not too many people are familiar with the name, nearly 70% of the population experience this phenomenon. It usually follows the same pattern: A person is just beginning to nod off. Their respiration and heartbeat slow down, the body temperature lowers, and the muscles begin to go slack in preparation for deeper sleep. It’s at this moment that the hypnic jerk strikes.
Researchers speculate that the slackening of the muscles create a sensation that the brain interprets as falling. This perception of danger then moves the brain to provide a visual backdrop for these sensations. This is not an actual dream (It’s not a product of REM sleep). It’s closer to a daydream or hallucination. And it usually fits the occasion: hitting the ground after a fall, having an object thrown at you, being attacked by a mandrill baboon.
Now comes the time to put the jerk in hypnic jerk. The brain’s final response to this perceived threat is to initiate an involuntary, and sometimes violent twitch, that usually awakens the sleeper (and sometimes their partner).
Though not much is known about what instigates this phenomenon, it’s generally thought to be intensified by anxiety, caffeine, stress, and strenuous activities in the evening. Hypnic jerks are considered a normal part of the many phases our bodies go through in preparation for sleep, and are regarded as harmless.
So the next time you find yourself awakened by such a violent jolt, you can take heart in knowing that this experience actually has a name, and that you’re not alone in this twitch inducing drama. Millions of others just like you, are imagining themselves falling, getting hit in the face, and being attacked by angry baboons.