I had one my junior year, which was not too serious, and the effects of it soon cleared up. However, the next year, I received a violent blow to the head (
football again)
in which my mouthpiece wasn't in correctly. I was wearing a revolution helmet, the supposedly concussion proof helmets, which cracked all the way down the side from where I got hit. I blacked out momentarily and got up a few moments later having little recollection as to what happened.