What can cause a concussion?

Impact to head: Concussion is due to the brain absorbing force in either a direct or tangential force that causes the brain to "slosh" around inside the skull. This can cause neurological deficits that are usually temporary. Repeated concussions can lead to permanent brain damage, especially if they occur repeatedly before the effects of the prior concussion has resolved. Rarely in this situation death can occur.

Blow to head: A blow to the head which causes a rapid movement of the head on neck causes the brain to deform a bit and temporally cause the brain and brain stem to deform, causing symptoms of a concussion. Headache is caused by the temporary injury to the headache center in the brain stem. Abdominal pain and nausea results from injury to the nausea and vomiting center in the same area.