A concussion is a brain injury that cannot be seen on routine x-rays. It can affect the way you think and remember things, and may have a variety of signs and symptoms associated with it. You do not have to be unconscious to have a concussion. Any blow to the head, face or neck or even to the body which causes a force to be transmitted to the head may cause a concussion.
Please refer to the following references for more information about concussions: