You should never ever, ever do any kind of breathwork prior to getting into deliberate cold ... If you're doing a lot of exhaling, you're blowing off a lot of carbon dioxide; that will limit your gasp reflex. And there have been people who have done, you know, cyclic hyperventilation, deep breathing, then gone into water, and they didn't realize that they needed to breathe. They didn't get that gasp reflex early enough, and unfortunately, they blacked out and died.