The 27-year-old had a cough and thought she had broken a rib, but in fact it was the painful lung infection, reported Mirror online.
"You do period films and you get some sort of weird archaic disease. And I didn't realise, so I went on for another month. I just stupidly never went to a doctor," she said.
"I was rehearsing for this play and 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 star went on a health kick afterwards, but with unexpected results.
"My body at the end of last year was breaking and I thought, 'I've really got to try and do something'. I've been trying to get myself into gear. I've been doing yoga, but I've already got injuries
