What exactly is a concussion? Do you have to be momentarily knocked out?

Concussion. Traumati brain injury that alters the way your brain functions is concussion.Effects are usually temporarybut can include problem with headache, memory, judgment, balance and coordination.Most of the time it is caused by a blow to the head but can be caused if upper part of the body is violently shaken.The injury can cause loss of consciousness but some people have mild concussion and dont know it.
Concussion. Closed head injury caused direct blow to head or sudden deceleration resulting in altered mental status. Symptom may vary or fluctuate (ie headache fogginess confusion). Loss of conciousness does not have to occur.