Unknown. Idiopathic myoclonic jerks occur just
prior to sleep and severely affect it. However, it disappears with the onset
of stage 1 REM (rapid eye movement) sleep. It is associated with a variety of conditions, including
iron deficiency, folic acid anemia, B vitamin deficiency, drug intake
(phenothiazine), barbiturate withdrawal, diabetes, renal insufficiency,
neuropathy, stroke, and chronic respiratory illness. It is common during
pregnancy and is precipitated by fatigue, anxiety, and stress.