The pregnant singer was struckdownwith the illness during her trip Paris, France, and admits she is feeling terrible.
In a series of posts on her twitter page, 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)"