A concussion is a traumatic brain injury (TBI) that may result in a bad headache, altered levels of alertness, or
It temporarily interferes with the way your brain works, and it can affect memory, judgment, reflexes, speech, balance, coordination, and sleep patterns.
Concussion - first aid
Causes, incidence, and risk factors
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 (called jarring) in any direction can cause you to lose alertness (become unconscious). How long you remain unconscious may be a sign of the severity of the concussion.
However, concussions don't always involve a loss of consciousness. Most people who have a concussion never black out. You can have a concussion and not realize it.