Natalie PortmanShortly before his death from prescription pills, Heath Ledger admitted to The New York Times that playing the deranged character of the Joker in 'The Dark Knight' haunted him so deeply that he stopped sleeping. Now it seems as though Natalie Portman can relate. She hints that she was traumatized as she grew into her disturbing role in 'Black Swan' as a ballet dancer who loses her mind.

"There were some nights that I thought I literally was going to die," she tells EW in its forthcoming issue. "It was the first time I understood how you could get so wrapped up in a role that it could sort of take you down."

Countless other stars have played mentally ill or downright psychotic characters: Jack Nicholson in 'The Shining,' Christian Bale in 'American Psycho,' Angelina Jolie in 'Girl, Interrupted,' Robert DeNiro and Johnny Depp in just about anything. And while those roles often win accolades, little has been made of the psychological impact they might have.

University of Pennsylvania psychiatrist Christos Ballas says there's no doubt that playing complicated characters can indeed be hazardous to your health.

"[There are risks] in taking on a really intense role -- it takes a toll on you," he tells PopEater. "The risk is they become the identity they're playing. What often happens is that they change. You're forcing someone to become someone else and then asking them to go back to normal."