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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.
Q: Why do I jerk before falling asleep? These involuntary muscle spasms are actually very commonâand harmless. Known as hypnic jerks or âsleep starts,â the spasms may make you feel as if youâre falling or have suddenly been âshockedâ awake.