By Kim Peiffer
Updated Nov 17, 2014 @ 11:55 am
Credit: Mike Coppola/Getty Images

Jennifer Aniston is already earning Oscar buzz for her turn in Cake, in which she plays a mourner suffering chronic pain, and last night we got a glimpse at her remarkable performance at a private screening hosted by The Cinema Society and InStyle’s Ariel Foxman (below left, with Aniston) at the Tribeca Grand Hotel.

“The experience has been extraordinary,” she tells InStyle exclusively. “It was a movie script that I read in about an hour and a half and within that time was sucker punched into it from the bottom of my heart. With every fiber in my body, I said 'I have to be able to play this part.'” And that, she did. Quite well, we might add. “I have had the most rewarding experience I’ve ever had,” she says.

Credit: Mike Coppola/Getty Images

The actress, who is keeping insanely busy in the midst of also promoting her film Horrible Bosses 2 (“I’ve had way more diet coke that any person should ever be allowed” she joked last night), says when it comes to looking well rested on virtually no sleep, there are three tricks up her sleeve that she's relied on over the years: “The gym, a lot of water and sleep as much as you can, and really give yourself the full 8 hours—that is, if you can get it!”

Sleep or no sleep, that didn't stop Aniston from hitting the town last night like a true champ. The actress later joined fiancé Justin Theroux and others at the screening after-party, a Grey Goose-sponsored fête at Jimmy at The James New York.

Cake, which premiered at the Toronto International Film Festival in September, will be in out in theaters for only one week in December before the film widens its reach to audiences in January, 2015.