I was once shoved underwater by a kid, and he kept me down there, couldn't breathe, obviously. Eventually, I shook him off, after about 45 seconds. Thought I could only stay under for about 30, managed to say alive. I was 7. Air, how I love you. Since that time, I have learned how to stay underwater for up to 2 minutes, no problem.
EDIT: Half-remembered another one.
I was maybe 4, and I was standing in a bus stop with my grandfather. he was talking to someone, and I was bored. I decided to lean on the glass side of the stop, like I did often. What I didn't notice, was that the window was smashed. I fell down, directly into the pile of broken glass on the floor, and got the wind knocked out of me by the metal bar that held the glass in place. Don't remember what happened then.
Another time was when I fell down some very, very high steps. Painfully. Hurt like hell, got home, and lay down. By the next day, I was fine.