Tim Minchin is worried. He may be a successful comedian, actor and composer, but he says he "just feels sick all the time" ahead of the world premiere of his new musical Groundhog Day. It opens at The Old Vic in London in August.
Minchin has written the score and the lyrics for the show, which reunites the creative team behind the musical Matilda and has been a huge hit on both sides of the Atlantic.
And although he insists he likes Groundhog Day "as much as Matilda", he is nervous about how the show will be received.
"I have not been sleeping and my guts are in a knot. It's hard," he says.
He has spent four years working on the stage version which is based on the film, starring Bill Murray, about a man who has to relive the same day over and over again.
Although Minchin thinks the film is "brilliant", he says he tries not to think about it and hasn't watched it since he embarked on the project.
He also believes the story of a man stuck in a time loop is actually more suited to the stage than the screen.
"The concept of a person trapped in a day, trapped in a world, the parameters of which they don't understand, it screams theatre," he says.
"It's like Waiting for Godot or Rosencrantz and Guildenstern are Dead. These characters, who have to find their way philosophically through a life that they don't comprehend.
"So I think Groundhog Day should be a piece of theatre. And then the question is, can you make it sing?"
It certainly posed a musical challenge, but not necessarily the one you might think.
Minchin says he has lost count of the number of people who have approached him and asked: "Groundhog Day, it's just the same song over and over again right?" He laughs weakly, but however flippant, the comment clearly frustrates him.
"Songs in a musical illuminate the state of mind of the person singing. The music can't repeat all the time because the state of mind of the character isn't the same.
"Even though there is repetition in the world that he is in, his state of mind alters dramatically and so what he sings is going to change. The idea that you are singing the same song is absurd."
The concept of Groundhog Day as a musical had been floated since the film was released in 1993. There had been rumours of various projects, with Stephen Sondheim working on one for a while. However none of them came to anything.
But Danny Rubin, who wrote the film - and now the script for the stage show - says he thought it would make a good musical "from the very beginning".
"I love musicals, I play instruments and write songs and I thought this was something that would be fantastic at some point," he says.
But he was in no rush because, he says: "I didn't want Groundhog Day to be the only thing I was doing in my life." Nonetheless he worked on a draft stage version on and off for 20 years.
He had more or less finished it when the director Matthew Warchus rang him to discuss the idea, so the timing could not have been better.
Bill Murray's performance was central to the film's success. But Rubin never doubted the musical could work without him.
"Bill was fantastic. He really defined the character and defined the movie," Rubin says.
However I always felt the story would withstand any number of ways of telling it. And the character didn't need to be Bill Murray.
"We've found ways to let the character be somebody else. There is a lot of Tim Minchin that comes through and may be some other aspects of me that come through as well. I think Bill will be pleased.
Producers say they "would love Bill Murray to come and see the show when it is ready and open".
"He will find a rich musical that builds hilariously and movingly on the film. We hope he likes it."
Rubin says he hopes the audience will like it too - and enjoy an experience that is even more fulfilling than watching the film.
Minchin, meanwhile, is asking people who come to see the show, to turn off their mobile phones and "turn your mind on".
"You can't have your phone on in a theatre. It's a horrible, disrespectful thing to do to be honest," he says.
"It's very hard for actors if people have got their phones on. I have been on stage and looked out and seen glowing faces.
"People are really thick about phones. I just wish audiences would engage."
Groundhog Day will run for 10 weeks at the Old Vic before, Minchin hopes, moving to Broadway.
"It will go if it's good," he says. "Work like this will live or die on its merits."