Because restless legs syndrome (RLS) and periodic limb movement disorder (PLMD) are so similar, and because they often overlap, patients and even doctors can confuse the disorders.

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RLS symptoms occur when a person is awake, and the condition can only be diagnosed based on what that person is feeling—not by a sleep study or an overnight observation. PLMD, described here, is what happens after a person falls asleep.

More than 80% of RLS patients also experience periodic limb movements, and they are occasionally treated together: Some of the remedies that ease the strange urges you have while you're awake also sometimes calm the movements you experience during sleep.

Many people without RLS still experience PLMD, however, and risk increases with age. A mild case may never affect you, while more serious symptoms may frequently wake you—or your bed partner, or contribute to poor sleep and daytime sleepiness.