According to reports, the Twilight star - who is still in hiding after boyfriend Robert Pattinson walked out of their home - has become a "nervous wreck" and is "living off a diet of cigarettes, Red Bull and crisps".
"She's been hiding out at the Los Angeles home of a producer friend and is looking pale and worn-out."
The source also said that the star was so "grief-stricken" that even when she tries to eat she is sick.
"Whenever anyone tries to push her to eat even a small bowl of soup, she either claims that she's just had something, which isn't true, or that she's nauseous and there's no chance of keeping anything down," they continued.
"Kristen is grief-stricken and has hit rock-bottom. In many ways, Kristen living off cigs and Red Bull is a way of punishing herself."
Meanwhile she is reported to be furious that she seems to be taking all the flack for the affar over Rupert.
"She's grousing that he's 19 years her senior and was 'in a position of power over her' ... being a director of a movie she had just shot and presumably someone she was going to work with again."
IN PICS: ROB AND KRISTEN'S ROMANCE