Getting Lindsay Lohan to do a cameo in Scary Movie 5 has become a scary ordeal for the film's producers, who have been jerked around by the actress.

According to Page Six, anyway. As the date for filming approached, Lohan allegedly disappeared, blew off rehearsals and missed her flight to the set.

She even bizarrely claimed she had walking pneumonia ... whatever that means.

Page Six claims LiLo “freaked” after seeing the script was poking fun at her but did report for work at the last minute after being threatened with a lawsuit.

“Lindsay missed every meeting she had for the film, including script reads and wardrobe meetings,” said a Hollywood insider of the oft-troubled actress.

“Then she missed her flight to Atlanta on Sunday to shoot the movie. The producers were getting signs that she's a mess, and would not be fit to work.”

Sources say Lohan wanted to back out because of the nature of her role.

“It went pretty hard at Lindsay,” said a source, adding the script features a kiss with Charlie Sheen, and “she’d been freaking out about it for weeks.”

“She’s been locked up in her room at the Bowery Hotel. She’s been in a tailspin. Even Charlie Sheen worried she might not be able to do the scene.”

Another source says Lohan said she couldn’t do the film since she had “walking pneumonia,” and went to a hospital Sunday to get her lungs checked.

“She is under contract - so to get out of it, she had to prove that she was sick,” said a source. “She tried to prove she has walking pneumonia.”

A rep for Lohan said, “These stories are untrue, and she is willingly fulfilling all of her obligations.” Lohan's rep? Definitely earning his paycheck.