The Air Balloon singer alerted her fans that she was unwell on Thursday morning, tweeting about her symptoms in the early hours.
I can't stop projectile vomiting,also temperature #poisoned 😷😷😷😰😰😰😰😓😓😓😓😓— Lily Allen (@lilyallen) May 8, 2014
"I can't stop projectile vomiting," posted Lily. "Also temperature #poisoned."
The mother-of-two then uploaded a picture of numerous water bottles as she attempted to quell her sickness.
"#SHEEHYDRATING #poisoned," Lily captioned the image, combining the word rehydrating with the name of her album, Sheezus — showing that her illness hadn't dampened her sense of humour.
Things took a turn for the worse for Lily, however, and she was then taken to hospital.
The 29-year-old posted a photo of herself in a hospital bed with the caption "#SHEEzUS in #SHOSPITAL," before reassuring her fans: "I'm fine though guys, just need some fluids cause I can't keep anything down. #dramz."
Lily Allen: "#SHEEHYDRATING #poisoned"
Lily's stint in hospital comes at a very busy time for the star. The Hard Out Here singer has been jetting between the US and UK promoting her new album and attending numerous glamorous events.
On Monday night she stepped out at the Met Ball in New York, before flying straight back to England to see Miley Cyrus at the 02 Arena, appear on Loose Women and Alan Carr's show Chattyman and enjoy a reunion with her husband Sam Cooper and daughters Ethel and Marnie.
Lily Allen: "This travel catching up with me"
Lily is due back in New York this week although given her poor health it is unknown whether she will be able to go.
Lily Allen at the Met Ball
The star also recently opened up about the trauma of nearly dying after losing her first child with husband Sam Cooper in 2010 and the therapy she had after.
Lily spoke with heartbreaking honesty about the miscarriage she endured when she was six months pregnant, and her subsequent battle with septicaemia.
"It was horrendous and something I would not wish on my worst enemy," Lily told The Sun on Sunday. "It's something that I still haven't dealt with, I never will get over it.
"…I held my child and it was really horrific and painful — one of the hardest things that can happen to a person. I was overwhelmed by what an incredibly unlucky thing it was to happen. But I had this man standing by my side, who I knew was going to be with me for the rest of my life."