Haha, concussions suck. I've had two concussions (that I can remember, anyway!). With the first one, I milked it for all it was worth and skipped school for a day and got a doctor's note so I didn't have to run the "mandatory" mile a few days later in PE class. I was swinging on one of those chinup bars that "anchors" itself inside of a door frame and it slipped lose, sending the back of my head into the concrete beneath me.
The second one: I was riding by bike at about 25 mi/h (spedometer said so, anyway) when I pulled into my driveway. I compressed the back brake, which produced a strange, intermittent sound (I later discovered it to be an obstruction in the rim of the wheel), which I, out of curious concern, turned around to briefly inspect. Little did I know, the dark had concealed the basketball pole about ten feet away from when I turned around to look. Needless to say, my head became close friends with the pole. I wandered inside with a lump the size of half a golfball on the side of my forehead.