Ryan Reynolds says the tumultuous, more than decadelong effort to make “Deadpool,” which went on to earn the biggest global box-office of any R-rated film, left him suffering panic attacks.

“I felt like I was on some schooner in the middle of a white squall the whole time. It just never stopped,” the actor, 40, says in the December issue of GQ, on sale Tuesday. “When it finally ended,” with the Marvel Comics superhero film completely recouping its production budget on the first day of release in February, “I had a little bit of a nervous breakdown. I literally had the shakes. I went to go see a doctor because I felt like I was suffering from a neurological problem or something. And every doctor I saw said, ‘You have anxiety.’ ”

Conceding how fortunate he has been in his life and career, Reynolds, who is currently developing the sequel for 2018, explained that “the attention is hard on your nervous system — that might be why I live out in the woods,” he said, referring to what Variety describes as an 8,892-square-foot home on nearly 12 acres in bucolic Pound Ridge, in Westchester County. “And I was banging the loudest drum for ‘Deadpool,’ ” his longtime dream project. “I wasn’t just trying to open it; I was trying to make a cultural phenomenon.”

Without describing what efforts he may have made to counter the anxiety, Reynolds — who recently become the father of his second child with his actress wife Blake Lively — told GQ, “My baseline’s pretty good, I think, aside from a few pretty intense anxiety hiccups over my life. I wouldn’t say I’m quantifiably happier now than I was when I lived in my . . . studio apartment on Wilcox in Hollywood. I’m also old enough to understand what’s an illusion and what’s real, and that it’s foolish to try to think that I can control anything from here on out.”