Just hours later, she had her appendix removed.
"Not gonna lie.... I may or may not have broken down in tears after the show from pain," she wrote on Twitter.
She flew home to Cedars-Sinai Medical Center, where she underwent surgery the next morning.
"Feeling awesome now," she added.
Clarkson's decision to perform while feeling ill could have been deadly, however.
Dr. Roshini Raj told Inside Edition that while the appendix is kind of a useless organ, it can become inflamed and burst, potentially leading to death.
Ahead of the show, Clarkson struck poses on the red carpet, beaming in Louboutin heels.
But, according to Raj, Clarkson must have been in a tremendous amount of pain, adding that people typically describe the symptoms associated with appendicitis as the worst pain they've felt.
For Clarkson, though, the show had to go on.