According to MTV:
Phoenix has said he's quitting acting to focus on his burgeoning hip-hop career. But with brother-in-law Casey Affleck following him around to film his every Andy Kaufman-esque move, speculation has been raised that the acclaimed actor is either having a public breakdown, suffering from a substance problem or playing an elaborate prank on the media for the purposes of the documentary.
I hope he's going to be okay. Joaquin is one of my daughter's favorite actors - she collects every movie he has been in.