Why Rihanna cancelled a concert in Sweden?

Rihanna has canceled a concert in Sweden tonight after being rushed to the hospital. The singer had been scheduled to perform in Malmö, but a representative for Live Nation said that she is "not in condition to conduct the concert" in a statement.

Earlier this afternoon, Rihanna tweeted an apology accompanied by a photograph of her arm with an I.V. tube. The nature of the singer's medical emergency is unclear, but in a tweet she wrote that playing the show "would have been a great time" and "so much better than being sick with the flu."