Keira Knightley caught a lung infection through over working.
The A Dangerous Method actress, 27, was struck by pleurisy last year - characterised by a pain when sufferers breathe - but at the time thought she had just hurt one of her ribs.
"You do period films and you get some sort of weird archaic disease," she said.
"And I didn't realise, so I went on for another month. I just stupidly never went to a doctor.
"I was rehearsing for this play and then I found in rehearsals it got so bad that I couldn't stand up any more.
"And they said, 'Please, can you go to the doctor?' "
The Holywood star has since turned to yoga to help keep her limber and functioning, but that has also resulted in a few injuries.
"My body at the end of last year was breaking and I thought, 'I've really got to try and do something'," she told the Australian edition of Harper's Bazaar magazine.
"I've been trying to get myself into gear. I've been doing yoga, but I've already got -injuries - from f***ing yoga."
Keira's most recent role was in an adaptation of Leo Tolstoy's epic novel Anna Karenina, in which she played the lead, a role which she described as the "hardest thing I have done to date", leaving her glad to let off some steam in the bar afterward.
"I'm s**t at karaoke, but on occasion [I like] a bit of karaoke. A good dance is necessary as well. Gin makes me cry though; I'm a vodka girl," she said.