Restless legs syndrome (RLS) is a disorder that causes a strong urge to move one's legs. There is often an unpleasant feeling in the legs that improves somewhat with moving them. This is often described as aching, tingling, or crawling in nature. Occasionally the arms may also be affected. The feelings generally happen when at rest and therefore can make it hard to sleep. Due to the disturbance in sleep, people with RLS may have daytime sleepiness, low energy, irritability, and a depressed mood. Additionally, many have limb twitching during sleep.