The Rude Boy singer, who was in New York for Monday night's Met Gala, responded to a fan's Twitter comment that she had been quiet all day with her most bizarre picture ever.
It showed medical tubes going into the singer's forearm – which is instantly recognisable from the black talons she wore to the costume ball.
She offered no explanation for the intravenous treatment but a US website has reported she was taken to a medical centre and treated briefly for 'dehydration' before being discharged.
The 24-year-old has been tweeting that she was sick in recent posts.
On Sunday she wrote: "F*** being sick."
And she added: "Seriously, I'm sick! Don't wake me up for dumb s***."
US reports also claimed she had angered bosses on Saturday Night Live at the weekend when she failed to show up to a final dress rehearsal.
She is thought to have sent her choreographer, Hi Hat, instead, claiming that she was too ill to attend.
A representative insisted that she was ill, saying: "Rihanna was sick and needed to save her voice for the live show."
Whatever treatment she was receiving yesterday for her unknown illness it seemed to do the trick and she was soon heading home to Hollywood.
She tweeted a picture of herself in front of a private plane, with the word: "My ride home. NY days LA nights."
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