What medical condition causes uncontrollable jerking movements of the arms/ legs?

Hypnic jerks. Jerking movements occurring as one is falling asleep are called hypnic jerks and are normal. Jerks during sleep may be periodic limb movements if they are repetitive, brief, and occur in series. If they cause poor sleep or daytime sleepiness, they can be treated, but they often occur in normal subjects. Jerks may occur with sleep apnea , parasomnias (abnormal sleep behavior), and seizures.