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Imagine that you're relaxed and drifting off to sleep when suddenly an arm or leg twitches and you have the sensation of falling out of bed. If this has happened to you, you've experienced what sleep specialists call a hypnic jerk or sleep start. Sleep starts happen in normal, healthy people and don't ordinarily require any medical treatment. However, certain medical conditions can make you jump in your sleep and should be evaluated by your physician.
Instead, hypnic jerks seem to be a sign that the motor system can still exert some control over the body as sleep paralysis begins to take over. Rather than having a single âsleep-wakeâ switch in the brain for controlling our sleep (i.e. ON at night, OFF during the day), we have two opposing systems balanced against each other that go through a daily dance, where each has to wrest control from the other.