It looks like that Denver air was just too much for Lady Gaga, who was hospitalized for altitude sickness after performing in Colorado.

Mother Monster, who performed a show at the Pepsi Center in Denver last night (Aug. 6), later Instagrammed one seriously close-up selfie of herself wearing an oxygen mask.

"Altitude Sickness is no Joke!" Gaga captioned the photo. "#hitThatHospitalS--- #artRaveDenver many true ravers [in the] crowd tonight."

While the main focus of the snap is undoubtedly Gaga's enormous mask, her insanely long eyelashes are pretty eye-catching as well, because we wouldn't expect her to go to the hospital in anything other than full makeup and an elaborate outfit.

Fortunately for the singer, she can take it a little easy today (Aug. 7), as she has a day off before her artRave show in Seattle, Wash. tomorrow night.

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