The 61-year-old actor, who has suffered from Parkinson's disease since he was diagnosed in 1991 at age 29, tripped and fell on stage on Sunday during a Back to the Future expo in Philadelphia. While on stage, the actor bowed to former Back to the Future cast members Christopher Lloyd, 84, and Tom Wilson 64, when he lost his balance and stumbled, landing on the nearby couch. The Stuart Little actor quickly recovered and continued a Q and A with his former co-stars.“Michael has Parkinson's. It's no secret that people with Parkinson's fall,” his rep told The Post.