"When he [George Clooney] left, I have never been hit with a depression like that," says
Bullock opened up to Variety about the film being just as emotionally taxing to film as it was physically.
One source of comfort - and eventually pain - was Bullock's co-star, George Clooney.
"Every single day. When George came, it was like an energy force and I was so appreciative of him being there," the actress explains. "But when he left, I have never been hit with a depression like that. We had so much fun for three weeks, but then my friend left. I was amazed at how I was affected by him going."
Bullock admits, "I had a hard time saying goodbye, I didn't want to look at him I just gave him a pat and he walked away and I was mad because I felt like everyday I was pushed against a wall with technology."
Despite "Gravity" using groundbreaking technology, Bullock says it wasn't easy to shoot the film alone in a box for up to 11 hours a day.
"I was angry at everyone who came up to me with a laptop to tell me where my hand had to be and where my head had to end up within a certain amount of time," she explains. "It was my job, with all of these constraints, to figure out how to be this person. I cut off all my sounds with ear wigs and the headpieces so I didn't have to be aware of teh technology that was happening around me."
Bullock, who stars alone in Alfonso Cuaron-directed film most of the time other than when she briefly shares the screen with Clooney, says that "breathing was our third character."
"We had a doctor that we talked to telling us what actually happens when these things happen, what happens to the eyes," Bullock says of what happens to humans if lost in space. "And I realized, 'I can't pretend that,' I'm going to have to do it every single day and that's when I would get the most frustrated because it made you light headed, you didn't have your bearings, you couldn't act while your peripheral vision was going but you had to get to that level so it looked right in the eyes and your skin did something special."
And it wasn't just a one time thing.
"Every day I would have to amp up to where I was before in the scene," she says. "We had to establish the level of panic and as it expressed the character's life or death struggles."
Watch Bullock explain the intense filming experience in her own words: