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, stumbling as she left the event early.
The candidate's team said she was diagnosed with pneumonia on Friday and given antibiotics, but had become dehydrated at the New York event.
Her doctor said she was now re-hydrated and "recovering nicely".
Mrs Clinton was due to leave for California on Monday morning for a two-day trip that included fundraisers and a speech on the economy.
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."
On Sunday, video showed her being supported by aides as they put her into her van after she left the 9/11 ceremony in New York early.
She was taken to her daughter's flat nearby and her team told reporters she was "overheated". The candidate 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, and on Sunday evening Dr Bardack issued the health update.
Her Republican opponents have queried her physical fitness, with the presidential candidate Donald Trump telling supporters last month she "lacks the mental and physical stamina" to serve as president and fight Islamic State militants.
Mr Trump's team has not yet made any comment on Mrs Clinton's pneumonia diagnosis.
Last month Dr Bardack said she 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 said.
The Clinton campaign has accused opponents of pushing a "deranged conspiracy about Clinton's health". Mrs Clinton is 68. Her Republican opponent Donald Trump is 70.
What is walking pneumonia?
Mrs Clinton's team say she is suffering with "walking pneumonia" - a less serious type of the lung infection which leaves patients feeling unwell but doesn't usually require bed rest or hospitalisation.
Pneumonia is essentially an infection of the lungs which causes inflammation in the air sacs and fills them with fluid. Symptoms can include a cough, fever, fatigue, chills and shortness of breath.
Anyone can contract pneumonia, although smokers, older people, and sufferers of chronic lung diseases are at increased risk. There are two types - bacterial or viral. Bacterial pneumonia is common and easily treated with antibiotics.
Most people with so-called "walking pneumonia" can recover within a few days. Those with weak immune systems or existing conditions can take weeks to recover, and pneumonia can in some cases be fatal.