Concussions range in significance from minor to major, but they all share one common factor — they temporarily interfere with the way your brain works. They can affect memory, judgment, reflexes, speech, balance and coordination.

Usually caused by a blow to the head, concussions don't always involve a loss of consciousness. In fact, most people who have concussions never black out. Some people have had concussions and not even realized it.

Concussions are common, particularly if you play a contact sport such as football. But every concussion, no matter how mild, injures your brain. This injury needs time and rest to heal properly. Luckily, most concussions are mild and people usually recover fully.