“Essential tremor” is the most common movement disorder. It is sometimes called “familial or hereditary tremor” because it is often inherited. The tremor usually affects the arms or hands. Tremor is the most obvious while the arm is in one constant or fixed position or when performing an action. Most individuals with essential tremor have a mild form, but others progress to severe “flapping” movements. Essential tremor usually affects both sides of the body and is made worse by stress or anxiety.