Paddy Considine's oxygen levels dropped to dangerous levels when he was acting out his death scenes in 'House of the Dragon'.
The '24 Hour Party People' star played King Viserys in the 'Game of Thrones' spin-off and the tragic monarch was seen entering a slow decline as he wasted away from a disease which caused his flesh to rot away - and Paddy says slowing his breathing down to portray the character's final moments made him feel ill for real.
He told Variety: "Playing somebody who’s dying is a strange thing, especially a prolonged death. When you do it over a period of days, and your breathing’s shallow - my oxygen level started to go down.
"I had to be taken off set and given regular fresh air, because I was nearly passing out. It’s almost like your brain starts to tell your body that you are sick. It’s really quite weird."
Playing the dying monarch also had an emotional impact on the actor as it reminded him of his own father's death from cancer - and he initially refused to watch the scenes when the show aired in the UK.
He added: "My wife and daughter watched episode eight when it aired in the U.K. I was in another room because I didn’t want to see it. My wife says: 'You’ve done the work. You need to see it', and she showed me the episode. The end, when he [King Viserys] lies in the bed, it was very shocking to me, because I looked the image of my dad when he was dying of cancer. The image of him."
Paddy went on to insist he loved starring in 'House of the Dragon' and was disappointed his character was killed off after just one season.
He added: "When series two comes around, I wish my comrades well, but there’s a hint of jealousy in there. Because I’m like: 'Ah, I don’t get to live it again'. But at least I got to tell a full story. He had a beginning and he had an end. And the end was pretty spectacular."