Hasn't there ben the occasional incident of someone trying to swim underwater, and in holding their breath they passed out?No, if you were mentally strong enough to hold your breath for a long time, you would just pass out, then you would start breathing again.
I understand of course that being underwater, and unconsciously breathing means you'll drown. But I thought it was more a case of brain damage due to the build up of carbon dioxide excluding oxygen.
I may be wrong, but I have a vague recollection of reading such stuff long, long ago.