Rihanna is believed to have fallen ill after "travelling nonstop" and "excessive partying".
The singer revealed she had been hospitalised in New York City earlier this week after posting a photo of an IV drip attached to her arm on her Twitter account.
Although she didn't confirm the reason for her stay, it has been reported that she was treated for dehydration after attending the Met Gala on Monday.
There is speculation that Rihanna's hectic work schedule and late nights have taken a toll on her health.
"[She became sick from] excessive partying and not slowing down. She has been travelling nonstop and going wild. Rihanna has been rebelling against her record label because she feels she has been made to work too hard," a source told New York Post.
"She's doing great now. She was super sick. She got some penicillin and an IV, and is better," another source added.
Although Rihanna dazzled in a Tom Ford black crocodile dress on the red carpet at the Metropolitan Museum of Art event, she wasn't spotted at the after-party at the Crown restaurant or the Prada bash.
The 24-year-old had been complaining that she felt unwell last week, often posting messages on her Twitter account.
She also sparked concerns for her health last weekend after pulling out of a dress rehearsal for US TV show Saturday Night Live due to illness.
"Rihanna did not do the dress rehearsal because of her throat, which was the first time that's ever happened," show creator Lorne Michaels told the publication. "I think for the live audience, when they heard that - we announced it just before she would have gone on - that also sort of took the air right out of the room. It was a very difficult dress [rehearsal] to gauge."
Despite her health scare, Rihanna shows no signs of slowing down.
It has been announced she will perform on the finale of American Idol on May 23.
Meanwhile, sources close to the Bajan star deny she is dating American football player Darren McFadden.
Wednesday, it was claimed Rihanna had been spotted making out with the Oakland Raiders star in Hawaii last month.
"Sources close to Rihanna tell us, the singer did meet Darren last month in Honolulu - while she was promoting her new film Battleship - but they kept things strictly platonic," reports TMZ.
The website adds that Darren was with his girlfriend when he met Rihanna and the trio relaxed on a beach over a few drinks.
