The 59-year-old actor was due to fly to the Arctic to star in and direct the movie but was rushed to the emergency room after suffering excruciating stomach pains. He was diagnosed with pancreatitis, which can be life-threatening.
George - who had lost almost 30lbs for the film - said: "I think I was trying too hard to lose the weight quickly and probably wasn't taking care of myself."
After being released from hospital, the Hollywood hunk still wasn't feeling 100 per cent, which made making the movie even tougher.
He said: "It took a few weeks to get better and as a director,it's not so easy because you need energy.
"We were out on this glacier in Finland, which made it a lot harder work. But it certainly helped with the character. This is bigger than anything I've done before and it was like herding cats to get it done. But, you know, it was fun."
As well as shedding the pounds to play a cancer-stricken astronomer, George stopped shaving for the role, which his wife Amal wasn't impressed with and their three-year-old twins Ella and Alexander were divided on.
He told the Daily Mirror newspaper: "I grew a big ugly beard and my son loved it because he'd hide things in it which I wouldn't know about until I got to work and I'd be like, 'Oh, there's a popsicle stuck in my beard'.
"But my wife and daughter were really happy when it came off because it was very hard to find a face underneath all that mess."