Why you have hypnagogic myoclonus
My cats twitch when they’re falling asleep. I thought they were dreaming of hunting mice. But I sometimes twitch just before falling asleep, and I don’t dream of hunting mice. This led me to a Straight Dope classic from 1981.
Dear Cecil:
Occasionally, just prior to falling asleep, I have experienced a jerk or twitch, as if my body is trying to reverse its inevitable slide into unconscious slumber. How do you account for this peculiar behavior? It’s also been known to happen to me when drowsiness overcomes me while listening to a particularly dry lecture.
— H.G., Chicago
Cecil replies:
Twitches while falling asleep are called hypnagogic myoclonus, myoclonus being any sort of involuntary muscle spasm and hypnagogic referring to sleep. The twitches occur during very light sleep as the conscious brain gradually relinquishes control of the motor functions. Often they’re accompanied by a sense of falling, or the feeling that something is flowing through the body, and sometimes people will experience vivid dreams or hallucinations.
It’s not known exactly what causes the twitches, but they appear to be associated (although by no means invariably) with (a) anxiety and (b) some faint stimulus, such as a noise. The twitches have been induced in test subjects who were instructed to push a button whenever they heard a low tone. When, as usually happened, the subjects nodded off after a while–you know how exciting psychology experiments are–the tone would often cause a subject to twitch after a lag of a few seconds…
Read The Straight Dope by Cecil Adams.
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March 29th, 2009 at 04:28
So this ” hypnagogic myoclonus” is pretty harmless, eh? When I was growing up and had them, my mother used to tell me these were sure signs I was growing up… in height.
The other phenom, involuntary leg twictches, if they occur incessantly while asleep, are a sure sign of another sleep disorder, called sleep apnea.