A concussion is a brain injury that occurs after physical trauma. A person may suffer a concussion after experiencing a blow to the head. Even if the head is not directly hit, a physical hit to the body can also cause the brain to take damage. These are usually associated with contact sports like football and ice hockey. Even with protective headgear, there is always a risk with rough high-speed activities. A concussion is the rapid movement of the brain inside the skull. Moving the brain rapidly causes it to move and twist. These resulting movements and twists are what damages brain cells. 
Concussions can result in short-term and long-term problems. In most cases, the effects of a concussion will for a few hours or a few days. But in more serious cases it can result in life-long medical problems. This condition is a mild traumatic brain injury (or a TBI). Mild because the symptoms are usually not life-threatening. The short-term effects include confusion and tiredness. These effects will usually occur soon after a person has experienced head trauma. Those who think they may be concussed should seek medical treatment ASAP.