"He's obviously a deep guy with some dark reference points," Drew said. "There's obviously a shadow over his life. He's had problems played out on the public stage."
In 2005, after filming the Cash biopic "Walk the Line," Phoenix entered rehab for alcohol abuse. He told reporters afterward that he started drinking more while playing Cash.
"It was then that I became aware of my drinking. I wasn't an everyday drinker but didn't have anything else to do, anything to hold me down," he said. "I was leaning on alcohol to make me feel OK. That's what it really was."
Publicist Patricola quashed any rumors that Phoenix is self-destructing.
She told ABCNews.com, "He is fine and doing his music," but would not go into detail. "When Joaquin has more to say, I'm sure he will," she said.
Snedegar said Phoenix appeared fine the night he performed. "Every time I spoke to him he was coherent, polite. He was low key but open to the fans."
Even though Phoenix's agent had booked the gig a couple weeks before, it was still undecided whether he would perform that night. The evening started with a specially prepared vegan dinner for Phoenix and 20 friends, including Affleck, at the Palazzo Resort Hotel and Casino.
The group then moved upstairs to Lavo, Snedegar says, where they sat at a table in front of a catwalk with a microphone, in case Phoenix decided to perform.
A member of Affleck's documentary crew gave the signal: Phoenix was ready to go on.
"I don't know if I would say he's a natural," Snedegar added. "He isn't horrible. He can keep on beat. He was kind of dancing and on rhythm and that was good."
Phoenix, who seemed tentative at first, Snedegar said, soon warmed up during the course of the three raps, strutting the catwalk and, by the end, jumping up and down and thanking his audience profusely. "You hold a very special place in my heart," he told the crowd.
Perhaps it was the adrenaline that made him miss a step as he was leaving the catwalk and fall into the audience, where he landed on his feet.
"He took pictures with fans, hung out another hour," Snedegar said. "His friends were hugging him. He seemed very happy."
And if it's all an act, another source told EW.com, don't expect him to break character any time soon.
"It's an art project for him," the source said. "He's going full out. He probably has told his reps that he's quit acting. Joaquin is very smart. This is very conscious. He has a huge degree of control."