I’m breathing in my own carbon dioxide. It builds up in the body and affects the muscles... You have to overcome all of that while you’re doing it, and be present.

"I had to train myself how to breathe. There were times I would pass out physically; I was unable to get back into the cockpit," Cruise says.

Tom Cruise told Empire magazine that he breathed in his own carbon dioxide while filming a grueling action set piece for the upcoming “Mission: Impossible – The Final Reckoning.” The sequence finds Cruise’s Ethan Hunt underwater exploring the wreckage of a submarine.