What causes the body to suddenly jerk during sleep?

A sudden body jerk during sleep is caused by sleep myoclonus or periodic leg movements. Sleep myoclonus is a normal limb twitching that occurs more frequently when one is fatigued, stressed, or has consumed excessive alcohol. Some people may experience a sensation of falling from a height, but there's no need to worry—this is a very common physiological phenomenon. Periodic leg movement disorder involves rhythmic, recurring jerking movements in the lower limbs. If these movements disrupt sleep, medical evaluation and treatment at a hospital are recommended.