Hillary Clinton's doctor has revealed the US Democratic presidential candidate was diagnosed with pneumonia on Friday.
The doctor's statement followed Mrs Clinton's early exit from a 9/11 ceremony on Sunday which had raised health concerns.
Statement from Sec. Clinton's doctor: pic.twitter.com/jyJLhddQJQ— Robert Costa (@costareports) September 11, 2016
She left the ceremony in New York because she had "felt overheated" and had gone to her daughter's apartment but later said she was "feeling great", her team had earlier said.
Mrs Clinton had a medical examination when she got back to her home in Chappaqua, New York, according to a campaign aide.
Her personal doctor, Lisa Bardack this morning (NZ time) said she had been experiencing a cough related to allergies and on Friday was diagnosed with pneumonia.
The statement comes at a crucial time in the presidential race as Mrs Clinton's Republican opponents have queried her physical fitness. Donald Trump and some of his high-profile supporters have repeatedly argued she lacked the "stamina" to battle adversaries abroad.
Mrs Clinton's doctors say she made a full recovery from surgery she underwent in 2012 for a blood clot.
Dr Bardack said last month she was "in excellent health and fit to serve as president of the United States".
The Clinton campaign has accused opponents of pushing a "deranged conspiracy about Clinton's health".
Mrs Clinton is 68. Republican candidate Donald Trump is 70.
Emerging from her daughter's home on Sunday, Mrs Clinton said: "I'm feeling great. It's a beautiful day in New York."
She later left for her home in Chappaqua, New York, according to her campaign.
A video posted on Twitter purports to show Mrs Clinton being supported by aides at the 9/11 ceremony before being helped into her van.
The statement from the Clinton campaign said: "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.
"During the ceremony, she felt overheated so departed to go to her daughter's apartment, and is feeling much better."
Mrs Clinton previously served as secretary of state and retains an honorary title.
The weather was warm and humid in New York on Sunday, and there was a breeze during the ceremony, the Associated Press reports.
The candidate came to the ceremony fresh from a political storm over comments she made about Mr Trump's supporters at a fundraiser on Friday.
She had apologised on Saturday for suggesting half of the Republican's supporters were "deplorables".
Mrs Clinton is scheduled to begin a trip to California and Nevada on Monday. She is due to appear on the Ellen DeGeneres Show on Wednesday and attend a rally in las Vegas on the same day.
Services marking the 15th anniversary of the 9/11 attacks have taken place in New York and around the world throughout Sunday.
A total of 2996 people died on 11 September 2001 when al-Qaeda militants hijacked four planes, crashing two into the World Trade Center's twin towers in New York, a third into the Pentagon and the fourth into a field in Pennsylvania.
Passions are high just over two weeks before the first election debate between Mrs Clinton and Mr Trump on 26 September. Election day is 8 November.
- BBC, Reuters