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 is no stranger to difficult stunts, as he's proven time and again in the Mission: Impossible franchise, but he might have faced his biggest challenge to date in the upcoming movie Mission: Impossible – The Final Reckoning.