Joaquin Phoenix faked downward spiral for two years for documentary

Concerns about the actor began after Phoenix appeared mumbling and confused on David Letterman’s chat show last year. It emerged that he was playing a character, the same character which features in the film ‘I’m still here’, where Letterman was not in on the joke.

Phoenix is shown in the film apparently taking drugs, surfing the internet for prostitutes and vomiting. Brother-in-law and film director Casey Affleck said the psychological meltdown of the actor during the documentary highlights his excellence as an actor.

"It's a terrific performance, it's the performance of his career," he told the New York Times.

Affleck said the bearded actor put his professional career on the line to star in the documentary, which also features rap artist Sean “P Diddy” Combs, who finally agrees to listen to a demo of his hip-hop music.

The film depicts funny and childish scenes as well as aggressive and often paranoid moments, struggling to live with the shock decision of abandoning acting to pursue hip-hop.

At the Venice International Film Festival this month, Phoenix swore it was a genuine documentary.

"I never intended to trick anybody," said Affleck.

Phoenix, who was nominated for an Oscar for his role of Johnny Cash in 'Walk The Line', is due to return to the Letterman Show next week, but will not be in character.