Myoclonic seizures are characterized by brief, involuntary spasms of the tongue or muscles of the face, arms, or legs. Myoclonic seizures are most apt to occur when waking after a night's sleep.

The medical phrase is "myoclonic tremor". It is caused by either an injury or condition that affects the nervous system, literally the nerves. Myoclonic tremor is often from a spinal injury. Myoclonic refers to the frequency and quality of the tremor, e.g. fast, slow, rhythmic, etc. Myoclonic can be further distinguished as tonic or clonic, which refers to the degree of musle rigidity that occurs during the myoclonic tremor. Note that the words jerk, jerks, or jerking are offensive to a person who has tremors.

myoclonic jerks often seen in eileptic patients

It is a myoclonic or hypnic jerk.

These are characterized by rapid muscular contractions accompanied with jerks in facial and pelvic muscles.