Doctors officially diagnosed Aniston with heatstroke after complaining of nausea and severe headaches and eventually fainting during filiming in Chicago, Illinois.
Sources working on the set, however, attribute the recent headlines revealing Aniston's ex-husband Brad Pitt accompanied his "Mr. and Mrs. Smith" co-star Angelina Jolie to Ethiopia as the cause of Aniston's emotional collapse. Jolie traveled to the third-world country to pick-up an orphaned baby girl she recently adopted.
Despite their repeated denials, Jolie and Pitt have been the topic of worldwide speculation they began a romantic relationship while shooting "Mr. and Mrs. Smith" - when Aniston and Pitt were still together.
Aniston divorced Pitt in January, Pitt has since been seen in various exotic locations with Jolie and her son, Maddox.
British newspaper, the Daily Mail, quoted an insider who says of Aniston, "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."
Aniston has recently refuted reports she was romantically involved with "Break Up" co-star, Vince Vaughn.
