Sylvester Stallone is reflecting on the making of his 1985 film Rocky IV in a new documentary.

The actor, 75, has released The Making of Rocky vs. Drago by Sylvester Stallone on his YouTube channel where he recalled his first day of filming a fight scene with Dolph Lundgren, who portrayed Rocky's main competitor Ivan Drago in the sequel.

Describing his first day of filming with Lundgren, Stallone said, "The first thing we shot [was] my entrance, his entrance and the introductions and then I got really injured during the fight and I had to be flown into intensive care to California from Canada."

Stallone said he had encouraged Lundgren, an actor and martial artist, to show his "dominance" in the scene against Rocky.

"Well, he pulverized me," Stallone said. "And I didn't feel it in the moment but later that night my heart started to swell. My blood pressure went up to 260 and I was going to be talking to angels, next thing I know I'm on this emergency, low-altitude flight. I'm in intensive care surrounded by nuns and then after that, I had to go back and finish the fight."

Stallone said he stayed in the intensive care unit for four days before returning to film the final fight in the movie. He also revealed that Lundgren's punch to his chest is "what's in the original movie."

"How could you take that out?" he said in the documentary.

Stallone encouraged fans to watch the documentary in an Instagram post on Tuesday, writing in the caption, "If you haven't seen this documentary, you should. If you really wanna know what goes on in the filmmakers mind, what really creates the amazing images, and hopefully the excitement …. So watch this documentary, I believe it's the best one ever done on the subject because you will be there in the moment. #YOUTUBE.COM/SLYSTALLONESHOP."