The actress appeared in Treats at London's Garrick Theatre on Saturday. The first show, due for Friday, was called off at the last minute amid rumours the Doctor Who star was either stressed out or ill.
Piper's agent told the Sunday Express: “Billie felt pretty unwell yesterday and was taken to hospital as a precautionary measure. She was not kept in and was quickly out of bed and up and around."
In response to speculation Piper is pregnant, she added: “I am not prepared to discuss any other rumours about her health as she is now purely concentrating on her role in the show.”
The Sunday Mirror reported the star was rushed to hospital on Friday night after collapsing in agony.