A concussion is a brain injury that can affect how your brain works. Concussions may happen because of a hit to the head, neck, face or somewhere else on the body that makes the brain move quickly back and forth inside the skull. The brain can become injured if this happens. Falling, being in a collision, playing sports or being hit by an object or person are some examples of actions that can cause a concussion. Only a medical professional (doctor or nurse practitioner) can medically diagnose a concussion.