Orthostatic tremor is a rare condition and the exact cause is unknown.
The symptoms are quite unusual. Although it is a form of tremor, people who have this condition don't always describe a tremor. Instead they feel unsteady when they stand in one place. The feeling goes away if they walk or sit down. The feeling of unsteadiness is often so uncomfortable that people with orthostatic tremor avoid standing still, such as in line in the grocery store.
Most people with this disorder also have a tremor in their hands.
Orthostatic tremor can sometimes be associated with Parkinsonism (symptoms that look similar to Parkinson's disease) or restless legs syndrome. While orthostatic tremor lasts forever, it usually does not get worse over time.
Unfortunately, no treatments have a great success rate. Clonazepam is the drug prescribed most often. It decreases symptoms in some people. Other drugs to consider include levodopa (Sinemet) and primidone (Mysoline).