In reflex epilepsies, myoclonic seizures can be brought on by flashing lights or other environmental triggers (see photosensitive epilepsy). Familiar examples of normal myoclonus include hiccups and hypnic jerks that some people experience while drifting off to sleep. Severe cases of pathologic myoclonus can distort movement and severely limit a persons ability to sleep, eat, talk, and walk. Myoclonic jerks commonly occur in individuals with epilepsy. Cause
Myoclonus in healthy individuals may indicate nothing other than arbitrary muscle contraction. Myoclonus may also develop in response to infection, hyperosmolar hyperglycemic state, head or spinal cord injury, stroke, stress, brain tumors, kidney or liver failure, lipid storage disease, chemical or drug poisoning, as a side effect of certain drugs (such as tramadol, quinolones, benzodiazepine, gabapentin, sertraline, lamotrigine, opioids), or other disorders. Benign myoclonic movements are commonly seen during the induction of general anesthesia with intravenous medications such as etomidate and propofol. These are postulated to result from decreased inhibitory signaling from cranial neurons. Prolonged oxygen deprivation to the brain, hypoxia, may result in posthypoxic myoclonus. People with benign fasciculation syndrome can often experience myoclonic jerking of limbs, fingers and thumbs. Myoclonus can occur by itself, but most often as one of several symptoms associated with a variety of nervous system disorders, including multiple sclerosis, Parkinsons disease, Alzheimers disease, opsoclonus myoclonus, Creutzfeldt–Jakob disease, Lyme disease and lupus. Myoclonic jerks commonly occur in persons with epilepsy, a disorder in which the electrical activity in the brain becomes disordered leading to seizures.
Myoclonus is a brief, involuntary, irregular (lacking rhythm) twitching  of a muscle or a group of muscles, different from clonus, which is rhythmic or regular. Myoclonus describes a medical sign and, generally, is not a diagnosis of a disease. These myoclonic twitches, jerks, or seizures are usually caused by sudden muscle contractions (positive myoclonus) or brief lapses of contraction (negative myoclonus). The most common circumstance under which they occur is while falling asleep (hypnic jerk). Myoclonic jerks occur in healthy people and are experienced occasionally by everyone. However, when they appear with more persistence and become more widespread they can be a sign of various neurological disorders. Hiccups are a kind of myoclonic jerk specifically affecting the diaphragm. When a spasm is caused by another person it is known as a provoked spasm. Shuddering attacks in babies fall in this category. Myoclonic jerks may occur alone or in sequence, in a pattern or without pattern. They may occur infrequently or many times each minute. Most often, myoclonus is one of several signs in a wide variety of nervous system disorders such as multiple sclerosis, Parkinsons disease, dystonia, cerebral palsy, Alzheimers disease, Gauchers disease, subacute sclerosing panencephalitis, Creutzfeldt–Jakob disease (CJD), serotonin toxicity, some cases of Huntingtons disease, some forms of epilepsy, and occasionally in intracranial hypotension.