Los Angeles: Pop star Rihanna struggled through illness to perform in Portugal and even ran off stage mid-set to vomit.

The 23-year-old Bajan beauty sang her hits to a sell-out crowd at Lisbon's Atlantico Arena, but the audience was left baffled when she disappeared during her performance of 'What's
My Name?', according to reports.

She took to her Twitter account after the gig to explain the incident, revealing she was feeling unwell during the concert.

In a series of posts, she writes, "Portugal tonight was legendary!!! I ran off stage to throw up, halfway through What's My Name... made it back just in time for Rude Boy," she

Rihanna appeared to be feeling better later.

"We just had our end of year/tour Christmas party!!!! We turned it into an 80's prom, since I've never had one! It was so much fun!!!! I'm decked out in lace, sequins, a giant bow, and hair spray," she added.