If he was holding his breath when he passed out he would start breathing again by default, with the regulator still in his mouth he would breathe and wake up again.

mabye he did hold his breath, but that cant be all of it. You cannot kill yourselve by holding your breath because of how breathing is a natural impusle. Try holding your breath for as long as possible and you'll realize that you will begin breathing again when your brain tells you to. So if he did hold his breath, he would have started breathing again and if he did, then we would still be alive. Our brains are are much more advanced than we think they are.