DefinitionA concussion is a brain injury that may result in a bad headache, altered levels of alertness, or unconsciousness.It temporarily interferes with the way your brain works, and it can affect memory, judgment, reflexes, speech, balance, coordination, and sleep patterns.See also: Concussion - first aidCauses, incidence, and risk factorsThere are more than a million cases of concussion each year in the United States.A concussion may result when the head hits an object or a moving object strikes the head. A concussion can result from a fall, sports activities, and car accidents. Significant movement of the brain (jarring) in any direction can cause unconsciousness. How long a person remains unconscious may indicate the severity of the concussion.SymptomsConcussions don't always involve