Mathew Horne has been in the West End play since January
Comic actor Mathew Horne has collapsed on stage during a performance of Entertaining Mr Sloane, forcing him to pull out of the West End show.
His co-star Imelda Staunton has also pulled out after feeling unwell and understudies will replace them both.
Gavin and Stacey star Horne fell to the floor in the middle of a scene and lay for 10 minutes before paramedics took him to hospital. He was later released.
His spokesman said he collapsed after working flat out for three months.
The actor will see how he feels on Friday before deciding whether or when to return, the spokesman added.
A BBC producer in the audience said he fell during a scene with actor Simon Paisley Day who called out for any doctors in the house to assist.
He was treated on stage before the manager asked the audience to leave London's Trafalgar Theatre.
John Rigby, a BBC producer in the audience, reported that Horne seemed "absolutely fine" during the first half of the Joe Orton play but that there was an unexpected delay after the interval.
It was announced the play would resume in three minutes but a further 10 minutes elapsed before the actors took to the stage.
Co-star Imelda Staunton apologised to the audience during the incident
Rigby said the audience seemed to be under the impression that Horne's collapse 15 minutes into the second half was part of the show until fellow actor Paisley Day called out: "I think something has gone wrong, is there a doctor in the house?"
One audience member came down to the front of the stage to help whilst another called out for someone to dial 999. An actor on stage replied: "Don't worry, it's been done".
The house lights were brought up and a further audience member asked whether the actor had been placed in the recovery position.
Several stage hands had come on stage to help out and one offered reassurance.
Horne fell with his back to the audience and did not move except to shake his head once while the ambulance crew were treating him.
While he was being treated, co-star Staunton walked on to the stage and apologised to the audience for the interruption.
She said that she had also been feeling unwell and was "incredibly sorry" for the events and the box office would repay the ticket costs.
She was interrupted three times by rounds of applause from the audience.
Rigby said: "I think everyone was just trying to show their concern for Mathew's wellbeing."
Horne was sending messages on his Twitter feed until the early hours of the afternoon. At 1400 BST he posted: "What a beautiful day!!! ... For doing a matinee and evening performance!"
The star, who is best known for the sitcom Gavin & Stacey, is currently starring on television and in film as well as on stage.
Horne & Corden, his sketch show with comedy partner James Corden, is running on BBC3 and the two can also be seen in cinemas in Lesbian Vampire Killers.