Recently I was in Hawaii, snorkeling in an area where I could walk around. I don't now how to swim, but I have been in shallow pools before. Unbeknownst to me, I was slowly drifting into a deeper area as I was busy just looking down at the fishies. Suddenly I realized my feet no longer could touch the bottom, and an initial panic set in. Then I quickly reasoned that I would just sink to the bottom (which was, about, 8 feet or so) and push myself off of it to reach the surface, then take a deep breath and do a doggie paddle-sort of a motion to get closer to the rocks nearby. If I had panicked, I would not have been able to hold my breath long enough. Luckily I did not at the moment and managed to reach the rocks (which were about 3 feet deep).
After that day, I swore to be more careful next time!