I am now imagining some truly improbable accident where a car drives into the water, hitting a shell, while a bike rides off a dock desperately trying to avoid the car... in a sort of Rube Goldberg symphony of exceedingly unlikely failure modes.

I'm not a particular fan of deep water, but it's not that much worse than shallow water if you mostly float. (Part of me still wants to take a freediving course somewhere warm. A lot of me is scared shitless by the prospect... which doesn't mean I won't do it....) I was severely disturbed when I went from default floating to default sinking, though. Do you default sink? You seem kinda muscley, so I could totally see it. (I felt betrayed by the transition... I have lungs *and* some breasts, and apparently that's not enough any more? WELL FINE. I thought women had to be, like, Olympic level athletes before they failed to float. Nope!)