Charlie Lawson believed he was suffering a "breakdown" in the build-up to starring in "Rebus: Long Shadows".
The "Coronation Street" actor - who is best known for playing Jim McDonald on the ITV soap - starred in Ian Rankin's play last year, and he says he became "physically and mentally exhausted" ahead of the opening night, on which he suffered a transient ischemic attack (TIA), also known as a mini-stroke.
In an interview with Stephen Nolan for BBC Radio Ulster, he said: "I hadn't been on stage for six or seven years, and you've got to scare the c**p out of yourself now and again and go back and do the stage, and this was guaranteed to be one hell of a scary time. But I was full of confidence."
Despite his confidence, the build-up also saw the original director of the critically-acclaimed stage show, Roxana Silbert, withdraw due to personal circumstances, and Charlie claims "from day one it was obvious" that the new helmer wouldn't have cast him.
Charlie said: "He didn't say that, but it was fairly obvious. And anyway, there was no relationship.
"That started to eat me up a bit when I wasn't working. It started to get into my soul a bit. I started not to sleep and I started to get very tired, and after three weeks" rehearsal I was pretty much exhausted already. That brings on anxiety, and it brings on worry about the part and all the rest of it."
Opening up about feeling vindicated after the show's previews received rave reviews, he said: "It meant the world, my confidence came back, everything that I'd lost, because I was working on thin air - I had no courage, I had nothing. Actors are very vulnerable, and you are out there on your own in front of 1,100 people.
"I never thought I was. I thought I was indestructible, but the whole experience brought me to my knees."
But in the days that followed, Charlie confessed he had to be taken to hospital by the company manager because he had struggled slept for weeks and believed he was "having a breakdown."
He said: "I felt like I just wanted to go home and do a runner from the theatre like Stephen Fry did. I knew I was physically and mentally exhausted, and I immediately phoned [partner] Debbie and said, "You've got to get here", I said, "I think I'm having a crisis, I think something's going to happen here."
"It has affected my emotional psyche. I consider that the way I was feeling mentally at the time I'm surprised that my brain didn't just explode, so I'm lucky. All the scans show that my heart is brilliant, there's no valve problem, there's no clot, it was down to stress. I'm angry about it, because I know why it happened. But I'll get over that."