A seizure is an involuntary muscle spasm, in a muscle group or the entire muscle system of the body. Convulsions can be caused by a neurological disorder affecting an area of the brain, a spinal cord injury, toxin, or syncope (cardiac discomfort). Tonic seizures, where the muscles are strongly contracted, and myoclonic seizures responsible for short and repeated shocks can be distinguished. Both types can be present within the same attack. The most common cause of seizures in children is epilepsy. Infants can also have seizures following a very high and sudden fever: these febrile seizures are usually harmless, but frightening for loved ones.