Hillary Clinton was diagnosed with pneumonia on Friday, and has been advised to rest and modify her schedule, her doctor said in a statement on Sunday.
The statement comes after the 68-year-old Democratic nominee left a 9/11 commemoration ceremony in New York City early on Sunday, after her campaign said she felt "overheated."
"Secretary Clinton has been experiencing a cough related to allergies. On Friday, during follow up evaluation of her prolonged cough, she was diagnosed with pneumonia,” Clinton's doctor, Dr. Lisa R. Bardack, said in a statement. “She was put on antibiotics, and advised to rest and modify her schedule. While at this morning's event, she became overheated and dehydrated."
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Bardack said Clinton is now doing much better.
"I have just examined her and she is now re-hydrated and recovering nicely," the statement concludes.
Clinton appeared to stumble and had to be helped into a van as she left the event, in unconfirmed video footage that surfaced on Twitter. She has now called off plans to fly to California on Monday morning for two days of fundraising, campaign events and an appearance on The Ellen DeGeneres Show, the Associated Press reports.
Clinton campaign spokesperson Nick Merrill said the former secretary of state had gone to her daughter Chelsea Clinton's nearby apartment after leaving the event at around 9:30 a.m. She was seen exiting the apartment at noon, and told reporters, "I'm feeling great. It's a beautiful day in New York," CBS News reports.
“Secretary Clinton attended the September 11th Commemoration Ceremony for just an hour and thirty minutes this morning to pay her respects and greet some of the families of the fallen,” Merrill said. “During the ceremony, she felt overheated so departed to go to her daughter’s apartment, and is feeling much better.”
Clinton's Republican rival, Donald Trump, has previously questioned Clinton's health. But on Sunday, he was mum about the incident, according to the AP. When asked by a reporter about Clinton's health scare, Trump reportedly said, "I don't know anything."
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ET caught up with Clinton in May, when she talked about facing off against the 70-year-old Republican nominee.
"I know a little bit about what it takes to be a president, and I think it's a risk to have a loose cannon like Donald Trump even coming close to running our country," she told ET bluntly. "So, the campaign is going to be about what kind of future we want, and how we're going to get there, and who's best prepared and equipped to handle all the responsibilities of the job."