Lily Allen Hospitalized After 'Projectile Vomiting'

Lily Allen was rushed to a London hospital Thursday morning after a bout of "projectile vomiting" ... but the singer insists she's fine.

Lily just posted the photo of herself on a hospital bed, plugged up with needles and tubes, along with the caption, "I'm fine though guys, just need some fluids cause I can't keep anything down."

Before she was hospitalized, Lily tweeted she couldn't stop "projectile vomiting" and felt extremely dehydrated. She had just appeared on British comedy show "Chatty Man" before falling ill.

Whatever it is, the sickness definitely appears sudden -- on Monday night, Allen was seen leaving the Met Gala in NYC scarfing pizza and looking healthy.