Correct. You'll start breathing after you black out. Also, you'll probably fail to even hold your breath that long. Takes training and a LOT if will power to be able to. You know that very uncomfortable panicky feeling that starts after a while when holding your breath? When that gets going for real, you are not even halfway to blacking out. Our body has strong feelings about breathing and is pretty good at letting you know how it feels about the lack of air. Or technically, the build up of CO~2~. You can somewhat bypass your body's CO~2~ detection by hyperventilation, but the end result is the same, you start breathing after you black out. Source: used to apnea dive, but as with everything I do, I quit before I got good.