The 32-year-old actor plays Jon Snow in the hit HBO fantasy drama, and got to ride one of the mythical beasts during the first episode of the eighth and final series, which aired on Sunday.
But he has now revealed that whilst filming the special scene, he managed to get his "right ball trapped" in the huge mechanical buck piece used to simulate the dragon on set, and thought the painful incident would kill him.
Speaking in a new behind the scenes video, he said: "Buck work is not easy. I think what sums up the buck for me was there was a bit where Jon almost falls off.
"The dragon swings around really violently, like this, and my right ball got trapped, and I didn't have time to say 'Stop!' and I was being swung around.
"In my head, I thought, 'This is how it ends, on this buck, swinging me around by the testicles, literally.' Sorry. Probably too much information."
Meanwhile, Kit recently slammed negative critics of the show, and said he doesn't "give a f**k" what they think, because he knows "how much work" went in to making the show.
He said: "I don't mean to sound mean about critics here, but whatever critic spends half an hour writing about this season and makes their [negative] judgement on it, in my head, they can go f**k themselves.
"I know how much work was put into this. I know how much people cared about this. I know how much pressure people put on themselves and I know how many sleepless nights, working or otherwise, people had on this show. Because they cared about it so much. Because they cared about the characters. Because they cared about the story. Because they cared about not letting people down.