Have you ever heard of myoclonus? A healthcare professional would define it as the quick, unexpected, short, and unintentional drying of the muscle(s). It relates to all groups of muscles. While some people wonder where the problem comes from, others know that various neurological issues often lead to myoclonus. It is rather a side effect than a separate illness. Between times, almost all people face this unpleasant condition.
Most probably, you have experienced a so-called “sleep start” at least once in your life. It reminds of the shocking spasm or cramp when getting ready for sleep or, vice versa, trying to wake up. It is one of the numerous forms of myoclonus. Even people without any problems suffer from this problem sometimes. When thinking about other examples, the first thing to come to mind is an abnormal startle. The worst type of the phenomena is the pathological myoclonus as it may disable the whole body for a while.