I got stuck inside an inner tube upside down in a swimming pool once and couldn't get out. There was no way to turn myself right-side up, either. I remember panicking, thrashing in the water upside down until I finally broke free and slipped out the underside of the tube. One of the scariest moments of my life and I think I was about 9 or 10 at the time. I still have these weird, recurring dreams that I've fallen face-down in a manhole and drown.
Side note: I seriously don't know how humans haven't evolved to be amphibious yet, what with "survival of the fittest" and all. We can create and perform the most extraordinary things historically, but still die in six inches of water. I'm sure it makes sense to biologists (or people with normal intelligence), but not to me.
It'll be awhile before I figure out how to do one of these. :P
