Restless legs
Restless legs syndrome (RLS) is a neurological disorder characterized by an irresistible urge to move one's body to stop uncomfortable or odd sensations. It most commonly affects the legs, but can affect the arms, torso, head, and even phantom limbs. Moving the affected body part modulates the sensations, providing temporary relief.
RLS sensations range from pain or an aching in the muscles to "an itch you can't scratch", an unpleasant "tickle that won't stop", or even a crawling feeling. The sensations typically begin or intensify during quiet wakefulness, such as when relaxing, reading, studying, or trying to sleep.
In the context of substance usage, certain compounds induce states of restless leg syndrome throughout the experience of them. This can be mild in its effects or extremely intense and uncomfortable.