US Democratic presidential candidate Hillary Clinton has cancelled a campaign trip to California after being diagnosed with pneumonia.
Mrs. Clinton was taken ill on Sunday at a 9/11 memorial ceremony and was seen stumbling as she left the event early.
Her doctor said she was now re-hydrated and “recovering nicely”.
Her Republican rival Donald Trump wished her a speedy recovery and promised to release details on his own health later this week.
Mr. Trump said health was now “an issue” in the election campaign.
Mrs. Clinton was due to leave for California on Monday morning for a two-day trip that included fundraisers, a speech on the economy, and an appearance on the Ellen DeGeneres Show.
Her personal physician, Dr. Lisa Bardack, said: “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. She was put on antibiotics, and advised to rest and modify her schedule.”
The candidate’s team initially said on Sunday she was “overheated”.
On Sunday, video showed Mrs. Clinton being supported by aides as she entered a van to leave the 9/11 ceremony after an hour and 30 minutes.
She was taken to her daughter’s flat in New York’s Flatiron building and re-emerged later on Sunday, telling reporters: “I’m feeling great. It’s a beautiful day in New York.”
She then left for her home in Chappaqua, New York.
Mrs. Clinton’s Republican opponents have queried her physical fitness. She suffered coughing fit last week at a campaign event in Cleveland, Ohio which fuelled speculation about her condition.
Last month, Dr. Bardack said in a letter that the candidate was “in excellent health and fit to serve as president of the United States”. She made a full recovery from surgery she underwent in 2012 for a blood clot, the doctor added.
But her Republican rival Donald Trump has repeatedly suggested she is unfit, telling supporters last month she “lacks the mental and physical stamina” to serve as president. -BBC