Yikes.

Lady Gaga shared a photo of herself wearing an oxygen mask early Thursday, telling her fans she was hospitalized for altitude sickness after her show in the mile-high city of Denver.

"Altitude Sickness is no Joke!" the songstress captioned the photo on Instagram. "#hitThatHospital[expletive] #artRaveDenver many true ravers crowd tonight."

The 28-year-old must be feeling a little better: Since sharing her hospital selfie, she's posted three pictures of her dog and one advertising her upcoming fragrance, dubbed Eau de Gaga.

Gaga is scheduled to play a concert in Seattle on Friday and a show in Vancouver on Saturday.