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A hospital visit is putting question marks over Lady Gaga's concert in Seattle tonight.  The pop star was hospitalized after her show in Denver Wednesday night with altitude sickness. 

Gaga posted a picture of herself wearing an oxygen mask and included the caption "Altitude Sickness is no Joke." 

Her next stop on her artRave tour is scheduled for tonight in Seattle. So far the show is still on.  Gaga was forced to scrap remaining dates on her tour last year after an injury forced her to undergo hip surgery. 

Photo: Getty Images