Jennifer Aniston talks about how she moved on from being a horrible, sex-crazed boss on "Horrible Bosses 2" to chronic pain-sufferer in "Cake," PEOPLE reported.

Aniston, 45, is being pitted for an Oscar in her upcoming performance in "Cake" as Claire Simmons, a role she said she was committed to from the moment she met with the film's director, Daniel Barnz. She talked about the process during a Q&A after the American Cinematheque screening of "Cake."

"I said to him, 'I have a whole plan', and he allowed me to go where I  wanted to go and we were together every step of the way," she said. "First, it was just understanding the logistics: what the accident was, where did the pain exist, what was the injury, getting into her voice, into her body."

The "Friends" alum's transformation into the dowdy Claire required a lack of make-up, darker hair and putting on a few pounds, according to Daily Mail.

"I knew that was coming. I basically didn't work out for two and a half months," she also said at the Q&A according to Daily Mail. "I stopped working out and I stopped being as careful about my diets as I normally am. I was still healthy, but I'd allow more."

She also said that it was refreshing having to go mostly without make-up during the shoot, save for the addition of darker rings under her eyes and the addition of the fake scar that her character sustained following the car accident.

"By the end, I didn't even notice they were there," she said. "And I also thought they were, I don't know, I thought they were kind of beautiful."

"Cake" is directed by Barnz and written by Patrick Tobin. It stars Aniston, Anna Kendrick, Sam Worthington, Adriana Barraza and more. It premiered at the Toronto Film Festival and is set for wider release on January 2015.