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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.
Another theory suggests that as youâre drifting off to sleep, your brain misinterprets the relaxing of your muscles as a sign that youâre actually falling and signals your muscles to tense up, in order to protect you. More often than not, hypnic jerks are nothing to worry about. If one wakes you up, simply roll over and go back to sleep. But keep in mind: a high caffeine intake, strenuous evening activities, emotional stress, or sleep deprivation may increase the frequency and intensity of hypnic jerks.