Myoclonus refers to a quick, involuntary muscle jerk. Hiccups are a form of myoclonus, as are the sudden jerks, or "sleep starts," you may feel just before falling asleep. These forms of myoclonus occur in healthy people and rarely present a problem. Other forms of myoclonus may occur because of a nervous system (neurological) disorder, such as epilepsy, a metabolic condition, or a reaction to a medication.