Tremor is the shaking movement of the whole body or just a certain part of it, caused by problems of the neurons responsible from muscle action. Tremor may occur as an isolated symptom and usually of unknown cause (essential tremor) or a part of the symptom constellation of another disorder (Parkinson's Disease). Tremors may occur at rest (Parkinson's disease), during voluntary movements (cerebellar lesions) or during excessive activity of muscles (essential tremor, hyperthyroidism). Tremors may increase with anxiety and caffeine and cease during sleep. Medications are used only if tremor interferes with daily life activities. Some of the drugs that can be used are clonazepam[?], mysoline[?], and propranolol.