Especially since if you're doing an emergency ascent, it's quite likely that it's due to having problems with getting air from your cylinder (if your air supply

Especially since if you're doing an emergency ascent, it's quite likely that it's due to having problems with getting air from your cylinder (if your air supply was fine, you'd probably be doing a controlled ascent instead). It's very difficult to avoid holding your breath when you know you won't be able to breathe in again until you reach the top.