I peed when I laughed... Is this normal?

I'm 15- and the joke wasnt even that funny! I didn't even know I had to pee! I stopped myself, and thank goodness it was at home, but it's happened at school before too. :/ I ddont wet the bed or anything so wtf is the issue here? Im worried. It was enough to leave a patch around my shorts:/ ughh.. I'm too old for this!