This is more similar to the accounts I've heard.
Did some more research into it and it seems if you go for the calm, hold your breath method, you can pass out before your lungs fill with water.. and then it's peaceful (although sounds like this is very difficult to do)
Also sounds that if the water is very cold and you hold your breath long enough that you do one big inhale, you get knocked out pretty immediately.
If you panic and don't aim to hold your breath... then it's a nightmare and you vomit and piss yourself and you may not pass out until your lungs fill with water which burns like hell. If you are in a "sinking" situation, you also have to deal with the pain of the water pressure.
Yeah.. drowning... so peaceful.