Denver's rarefied air seems to have gotten the best of Lady Gaga.
The "Applause" singer, who is currently touring with her ArtRave: The Artpop Ball, tweeted that she went to a hospital for a bout with altitude sickness after her Wednesday concert at the Pepsi Center.
"Altitude Sickness is no Joke! #hitThatHospital... #artRaveDenver many true ravers crowd tonight," the 28-year-old wrote on Instagram, posting a photo of herself in an oxygen mask.
No, it wasn't one of her cockamamie costumes, though would anyone have been surprised if it were?
Still, it probably wasn't her idea of a swell souvenir from the Mile High City.
The air is thinner and drier in the Colorado capital, and symptoms related to altitude sickness can include headache; anorexia, nausea or vomiting; fatigue or weakness; dizziness or lightheadedness; and difficulty sleeping, according to the National Library of Medicine.
It's unclear what Gaga dealt with, but ways to prevent such illness include drinking water, monitoring alcohol intake, eating potassium-rich foods and monitoring physical activity, according to a Denver trip-planning website.
Last year, country star Carrie Underwood had to have an oxygen break in her dressing room because of a similar episode.
A rep for Lady Gaga did not immediately respond to Los Angeles Times requests for comment.