The actor, who plays Jim Branning on the BBC One soap, was admitted to the Lister Hospital in Chelsea, West London, amid fears that he had suffered another stroke. It was later stated that he was in a "comfortable" condition.
Bardon has spent a year in recovery after having a stroke in July 2007. He recently filmed a one-off EastEnders episode, which airs on Monday, and had been looking forward to making a permanent return.
Speaking about the actor's condition in May, Bardon's wife Enda revealed: "John's speech comes out as gobbledygook. But he can swear! I hope being with his colleagues will get more out of him."
A month later, Bardon made his first public appearance in a year at the Life After Stroke Awards. A spokeswoman for The Stroke Association confirmed that he had made an "amazing recovery".