LONDON (Reuters) - Two psychologists said on Monday that leading actors — from Charlton Heston to Daniel Day-Lewis — have fallen prey to "possession syndrome" and cannot separate their roles from real life. Soap opera stars are among the leading victims of this thespian identity crisis along with method actors encouraged to immerse themselves totally in a part. Glenn Wilson and Andy Evans from London‘s Institute of Psychiatry found in research for a new book — "Fame: The Psychology of Stardom" — that fictional alter egos could end up dominating the actors who played them. "One of the problems that actors face is an identity confusion. They lose track of who they really are," Wilson told Reuters in an interview. He cited the case of Daniel Day-Lewis playing Hamlet in 1989. He got horribly confused on stage between the ghost of Hamlet‘s father and the ghost of his own father, Cecil Day-Lewis. "His personal life intruded. He could not carry on in the part," he said. Another case was Charlton Heston playing the stage role in London of Captain Queeg in "The Caine Mutiny". "He supposedly got so absorbed in the role that the character did nothing that surprised him. He would not know which was which," he said. Method actors were particularly prone to blurring the edge between fiction and reality. "They get started by doing this deliberately — absorbing themselves. But then it gets out of hand," Wilson said. Soap stars not only have to face the difficulty of not blurring their real and screen personalities, they can also suffer abuse and aggravation from fans who believe they are the characters they play. "Performers have been abused or thumped for something done in recent episodes. Other people have difficulty distinguishing," he said. But he cited the case of a Brazilian soap actor as the most tragic example of "possession syndrome." "A young actor killed his on-screen girlfriend because their on-screen relationship had ended. He actually stabbed her to death in real life," he said.