Rihanna was rushed to hospital after performing in Switzerland on Monday night (April 19, 2010).
The "Umbrella" singer played a sold-out concert in Zurich but after leaving the Hallenstadion venue just after midnight she was taken to the Hirslanden private clinic via a blacked-out Mercedes.
The 22-year-old pop star was then quickly escorted into the accident and emergency department by her driver, bodyguard and assistant to be treated for a mystery ailment.
Alenka Ambroz, head of the clinic's corporate communications, told Blick: "Rihanna arrived at the accident and emergency unit. We're not going to give any details."
She left the hospital at around 2.55am, over two and a half hours after being admitted, and was taken back to the venue.
It seems Rihanna's mysterious medical problem hasn't had any long-lasting effects though as she was able to take to the stage in Lyon, France, last night (April 21, 2010).
Rihanna's "Last Girl On Earth" tour is her most ambitious yet and features a number of costume changes and rigorous dance routines.
She recently said: "We've never done a tour to this capacity. The production is unbelievable and so are the costumes, we just took it to a whole new level. We just keep growing."
