A concussion may result from a fall in which the head strikes against an object or a moving object strikes the head. Significant jarring in any direction can produce unconsciousness. It is thought that there may be microscopic shearing of nerve fibers in the brain from the sudden acceleration or deceleration resulting from the injury to the head.

The length of unconsciousness may relate to the severity of the concussion. Often victims have no memory of events preceding the injury or immediately after regaining consciousness with worse injuries causing longer periods of amnesia.

Often the maximal memory loss occurs immediately after the injury with regaining of some memory function as time passes. Complete memory recovery for the event may not occur.

Bleeding into or around the brain can occur with any blow to the head, whether or not unconsciousness occurs. If someone has received a blow to the head, observe closely for signs indicating possible brain damage.

Things to watch for include repetitive vomiting, unequal pupils, confused mental state or varying levels of consciousness, seizure-like activity, weakness on one side of the body or the inability to wake up (coma). If any of these signs are present, contact your health care provider promptly.