The pregnant singer was struck down with the illness during her trip Paris, France, and admits she is feeling terrible.
In a series of posts on her twitter page this morning (05.10.10), she wrote: “I have the sorest throat ever. It's woken me up and I can't get back to sleep. Can't swallow, might die. X.
“Tres excited for Chanel this morning. Sore throat no better though. Full on flu.”
Lily – who attended the Chanel show today – has now left the French capital to go home to recuperate.
The 25-year-old singer has had a mixed time in Paris.
The pop star - who recently opened her own vintage clothes store Lucy in Disguise – was in France for a few days to attend a number of fashion shows, including Givenchy's Spring/Summer 2011 collection.
However, she was panicked by the British government’s “high threat” terrorist attack warning which advised people not to travel to France, and her fears were heightened by a suspicious man who sat next to her at a taxi rank.
Writing on her twitter page, she said: "Oh god, foreign office have put people travelling to France on high terror alert!!! I'm in Paris already. Scared being here but scared to get on the Eurostar home.
"Come to think of it. The day before yesterday there was this weird guy balancing a small bottle of something on his knee. He was sat next to me at a taxi rank, I thought he was being strange so I snuck a picture. I hope I'm just being a mad paranoid pregnant lady and that he wasn't a terrorist about to unleash deathly virus. (sic)"