Jennifer Aniston Collapses on Break Up Set  7/8/05

Actress Jennifer Aniston has collapsed on the set of her new movie The Break Up after complaining of nausea and severe headaches.

The former Friends star was officially diagnosed with heatstroke, after she fainted during filming in Chicago, Illinois.

But sources on set insist the star passed out because she was overcome with emotion, after it was revealed her former husband Brad Pitt had fuelled rumors he's dating Angelina Jolie, by accompanying her to Ethiopia, where she adopted an orphaned baby girl.

Jolie and Pitt have repeatedly denied reports they are a couple since Pitt and Aniston ended their marriage in January (05), despite numerous photographs of the Mr and Mrs Smith co-stars holidaying with Jolie's son Maddox.

An insider tells British newspaper the Daily Mail, "She's been walking around with a sad look on her face and has not been her usual self.

"While her collapse was blamed on heatstroke, everyone thinks it's more down to stress than anything else.

"She can't have escaped all the stories about Brad and Angelina and it looks like the situation has taken its toll on her."