Periodic limb movement disorder (PLMD) is a condition in which a person's legs, and sometimes arms, move repetitively and uncontrollably while he or she is asleep. These episodes of limb movement can disrupt the person's sleep, causing insomnia or daytime sleepiness. Periodic limb movement symptoms are only thought to be a disorder (PLMD) when insomnia or daytime sleepiness cannot be explained by any other problem, such as restless legs syndrome. Recently, it has been found that these movements are often linked to subtle breathing problems.