Josh Hartnett started hallucinating while filming '6 Below' due to his weight loss.
The 39-year-old actor is currently starring in the new film about real-life snowboarder/hockey player Eric LeMarque, who was stranded for eight days in a massive winter storm, and during filming Hartnett wanted a realistic performance and lost a dramatic amount of weight but almost lost his mind.
Speaking to the Metro newspaper, she said: "Because Eric lost weight on the mountain, I was on a diet that was minuscule.
"The amount of food I was eating was almost non-existent. So along with expending all this energy in high altitude, I wasn't taking anything in, so I was losing my mind from the hallucinatory effects of weight loss."
The film - helmed by Scott Waugh - tells the dramatic story of LeMarque who, after being stranded in a mountain, starts coming to terms with his own demons and rediscovers the power of faith while fighting for survival.
Not only did Harnett nearly lose his mind while film in the high altitudes of the Utah mountains, but the actor admitted he also had the beginnings of frostbite.
He said: "The cold up in the Utah mountains was uncomfortable but you can dress in layers of things underneath what the character's wearing that can deal with that. You're not immune to the cold when you're up in those elements. There's always cold that will be beyond your breaking point - but there were ways of dealing with it.
"At one point, I had the beginnings of frostbite and we had to stop filming so I could warm up. Medics wanted me to stop for a couple of days while my feet thawed but it wasn't possible so we had to put in more of those breakable heat pads in my boots and make sure I took breaks to warm up."
Hartnett stars alongside Mira Sorvino, Sarah Dumont and Jason Cottle in the new survival drama.