I'm usually pretty quick to jump in and help. Dragged an old dude out of the surf in Hawaii when the waves just kept knocking him down. I was watching him for 20-30 seconds and every time he'd get to his feet another wave would knock him down, he'd go under, come back up, get to his feet, cough up some water...repeat. After about 3 of those cycles I got to him and got him to the beach.
My most Aggie related experience of this sort was at the big Aggie tube trip 5 years ago or so. Saturday evening back at the Camp Warnecke pool, everybody was hanging out, eating/drinking, etc. and I noticed a woman at the bottom of the pool. Face down, looking pretty lifeless, but I didn't know if she was just messing around or not. So I went over to her and sort of nudged her with my foot to see if she'd respond, nothing. Like kicking, well, an unconscious person; no reaction at all. So I dove down, grabbed her under her arms, and brought her to the surface. Started yelling for help and for someone to dial 911 as I took her to the side of the pool, and then, with several other people's help, we got her out and onto the pool deck (she was not a small woman). She wasn't breathing and her lips were blue, but after maybe 15 seconds or so she coughed up some water, bile, beer, who knows, and started breathing again. Apparently she had been drinking all damn day and probably passed out while in the pool and just went under; no telling how long she'd been under when I saw her, but I'd guess a good minute or two. Oh, and I'd been drinking all day myself and have never sobered up so quickly before or since.