A source tells ET that the 22-year-old model was hospitalized over the weekend prior to attending the Vanity Fair Oscars after-party on Sunday. According to the source, Jenner had a bad reaction to a vitamin drip, resulting in a trip to Cedars-Sinai Medical Center in Los Angeles.
"She was working hard and took a vitamin drip over the weekend and had a bad reaction," the source says. "Kendall checked herself into Cedars and quickly bounced back."
"Kendall works so much and was exhausted so she got a vitamin drip as she often does," the source adds. "Things didn't go as planned but she was able to pull it together and look incredible at the Oscars after-parties."
As for Jenner's rumored relationship with NBA star Blake Griffin, the source says the two are keeping a low-profile after Griffin's less than amicable split from his ex-fiancee, Brynn Cameron. Last month, Cameron filed a palimony lawsuit against Griffin -- whom she shares two kids with, daughter Finley and son Ford -- claiming he abandoned his family for Jenner.
"They are laying low after his ex filed [court] documents about him leaving her for Kendall," the source says.
Though she was recovering from a trip to the hospital, Jenner looked amazing at the Vanity Fair after-party on Sunday, rocking a plunging black Redemption mini-dress with dramatic sleeves.
An eyewitness tells ET that Jenner looked "happy and healthy" at the party.
"I would have never been able to tell that she was hospitalized prior," the eyewitness says. "She appeared to be having a great time with model pal Joan Smalls; laughing and mingling with party-goers."
But Jenner's recent hospitalization isn't the first time the model has struggled with health issues. In an episode of Keeping Up With the Kardashians that aired last month, her mother, Kris Jenner, offered to take her to the hospital after receiving a worrisome phone call from her. Later, during an on-camera interview, the mom of six opens up about Kendall's anxiety.
"I think she has so much going on that she gets herself really worked up," she noted. "Kendall gets the most anxious during fashion weeks and when she's traveling a lot. ...Trying to juggle it all is overwhelming."