Sandra Bullock: Filming "Gravity" was "lonely" and "dark"

Sandra Bullock is getting a ton of positive buzz for her portrayal as Dr. Ryan Stone in Alfonso Cuaron's "Gravity," in which she plays a medical engineer on her first Space Shuttle mission who gets stranded in space alongside veteran astronaut Matt Kowalsky (George Clooney) with limited air.

But according to Bullock, the experience of filming was "lonely," and "dark."

"No one's with you, absolutely silent for hours and hours and hours on end," she revealed to ET about filming in such an enclosed space, at the film's Toronto International Film Festival premiere Sunday. "You realize what's in your head. After about the first 15 minutes, you go, 'OK, it's just going to be me, with me.' And you realize there's a lot of things in your head that don't need to be there. So it's isolating, but it ended up working for the film, so that's a good thing."

Pics: Sandra and her adorable baby Louis!

But on a lighter note, she enjoyed her adorable son Louis' reaction to her astronaut role.

"He remembers me as an astronaut -- it was two years ago -- he has a doll from it. He can't remember why he remembers me as an astronaut, which I appreciate," she said. "He has no idea what I do for a living. We like to keep it that way for like, as long as possible, and then he'll be just like, horribly embarrassed. I was his favorite superhero until this past week and then it went to Spider-Man. And I was like, 'Ohhhh, it's happening isn't it?'"

ET also caught up with Cuaron, who reacted to James Cameron's praise of the film as the "best space film ever done."

"Well I'm very grateful, I think that James is very kind and very generous," he smiled. " ... Films like this film and 'Life of Pi' wouldn't exist without James Cameron opening up the doors for this media."

Video: Sandra & George debut "Gravity" in Venice

Check out the video to hear his thoughts on Sandra and George Clooney's "dangerous" chemistry.

"Gravity" hits theaters Oct. 4.