Myoclonus is a rapid involuntary twiching of muscles. Myocloni are a side effect of many neurological conditons, but they can also happen in healthy people. As an example, twiching muscles when falling asleep are normal. Mycloni are a common symptom of epilepsy. Other less common diseses that provoke myocloni include encephalitis, Tics, and certain types of porphyria.