Convulsion refers to a sudden attack involving uncontrollable muscular contraction and relaxation. The person experiencing the convulsion may appear to shake uncontrollably, and the convulsion may include either a part of the body or the entire body.
Convulsions are a common manifestation of seizures in epilepsy, although some seizures do not involve any visible motor symptoms. Convulsions may also be caused by various conditions including meningitis, brain lesions, fever, and various kinds of poison, such as strychnine or cyanide poisoning.
If you observe someone having a convulsion, the most important thing is to protect the patient from injury. Cradle the head or place something soft underneath it, remove any nearby sharp objects, and loosen tight clothing -- but do not try to hold the patient still. Do not put anything into the mouth; people cannot "swallow" their tongues. However, the head can be turned sideways to allow the tongue to fall away from the airway.