Generally, if the jerking does not interfere severely with sleep patterns, it is nothing to worry about. Some types of jerking may be a sign of a more serious problem.
Benign sleep myoclonus
Some newborn babies may twitch or jerk their limbs in sleep, which can be very frightening for the parents, especially if it is their first born. It is understandable because this jerking may resemble a seizure due to a neurological disorder. Generally speaking, if the jerking stops when the baby is awake, it is not a seizure, so it is recommended that parents gently wake up the baby if they suspect he or she may have a seizure. It is better to do so than to just assume it is a seizure and expose the baby to unnecessary and often harmful medications.
Benign sleep myoclonus usually stops by itself by the time the baby is three months old. It is not certain why this happens but the scientists think it may be due to the fact that sleep cycles in infants need some time to adjust, which happens approximately around their 12th week.
Periodic limb movements of sleep
Periodic limb movements of sleep or PLMS are jerks that occur during the non-REM stages of sleep. Unlike hypnagocic myoclonus, which interferes with falling asleep, PLMS wakes up the person who is already sleeping. The episodes can last from a few minutes to one hour. The movements are usually small and sometimes barely noticeable, like Flexing a toe or bending a knee. It is not rare that a person who is having PLMS does not even know about it and only hears about it from their bed partner.
However, if the movements are sudden and heavy and if the episodes recur night after night, they may disrupt the sleep, resulting in daytime sleepiness, drowsiness, impaired memory or concentration, irritability, anxiety, and depression.
PLMS can be diagnosed in a sleep lab with the use of polysomnogram. By monitoring the sleep patterns, movements and brain waves doctors can diagnose specific sleep disorders. In case pf PLMS the therapy may consist of sleeping pills, narcotic painkillers or anti-seizure medications.
Factors that may increase the risk of PLMS include other sleep disorders and certain medications, like lithium, anti-nausea drugs and some anti-depressives.