Orthostatic tremor is a rare neurological condition characterized by a rapid tremor in the legs and trunk when standing upright, particularly in the lower limbs. The tremor usually occurs when a person is standing still but may improve when they start walking. It typically disappears when the person sits down or lies down. The condition can be disabling and affect a person's balance and gait. The exact cause of orthostatic tremor is not well understood, but it may be related to dysfunction in the cerebellum, the part of the brain that controls movement and coordination. There is no cure for orthostatic tremor, but treatments such as medications or deep brain stimulation may be helpful in managing symptoms.