Karl,
technically it takes up to 20-40 seconds for our brain to die (clinical death) from lack of oxygen and blood supply.
So, unless you have massive injury to head first - you'll most probably get your 30 seconds and feel lucky.
But can you elaborate your last statement ? As compared to what ? Just curious.

I must admit, this thread turned somewhat creepy. Good thing about sailing is that you can forget about all the crap going around the world while out there.