Once while diving in the Keys (maybe two years ago) I did a few days worth of dives, then took a break and the next day I spent at the "beach" with my wife (and of course I took my mask, snorkel, and fins...) I was doing a little freediving behind some rocks where I saw some shadows down below, About the third of fourth time down, I (not thinking) took a breath from my snorkel (at about 15 feet) The mouthful of water made me quickly aware that I wasn't using a reg...I usually used my "dry" snorkel which closes shut when you try to breathe in at any depth, but this time I just used the "tube" I use (well used to use) when diving...
Other than that...just bungy-ing myself to the boat after a surface interval!