The 28-year-old singer took to Instagram to share a close-up photo of herself wearing an oxygen mask, reported Ace Showbiz. "Altitude Sickness is no Joke! #hitThatHospital. #artRaveDenver many true ravers crowd tonight," she wrote along with the picture.
This is not the first time Gaga was hospitalised. Back in April, the 'Poker Face' hitmaker underwent an operation to extract her wisdom teeth.
Gaga's next gig in Seattle, as part of her 'ArtRave: The Artpop Ball' tour, is still scheduled to go on as planned.