concussion
n. mild injury to the brain, due to mechanical trauma or acceleration–deceleration injury, that disrupts brain function but is typically followed by spontaneous recovery. Concussion usually involves at least brief unconsciousness, although it may be diagnosed in the absence of unconsciousness. The symptoms may include memory loss, headache, irritability, inappropriate emotional reactions, and changes in behavior. Concussions may be classified by severity based on the period of unconsciousness or the extent of memory loss for events before and after the trauma. See head injury.