Ouch!! I've had that happen once, except to my toe nail lol. I was in a bad mood because my mom was annoying me (I was about 6 or 7) and my cat came in my room and I didn't want her in, so I shut the door, and my foot was in the way, and...yeah, you know. It hurt so bad! It grew back, but was black for a while which was totally gross, but now both toenails are as normal as ever. Lol, sorry if that story was a little too descriptive.