Heidi M Przybyla, and Eliza Collins

USA TODAY

Hillary Clinton was suffering from pneumonia when she quickly departed a Sept. 11 memorial ceremony in New York City on Sunday, according to her doctor, an episode that may intensify calls for a fuller release of both candidates’ medical records.

Clinton's physician, Lisa Bardack, said she had pneumonia and was recovering, though on Sunday night spokesman Nick Merrill said the candidate canceled plans to go to California on Monday and Tuesday.

Clinton attended the ceremony earlier in the day for an hour and 30 minutes before “she felt so overheated” she departed for her daughter’s apartment, Merrill said in a statement. The candidate later exited the apartment saying “I’m feeling great” before leaving for her home in Chappaqua, N.Y.

Once she returned home, Clinton was examined by her physician, who issued a statement saying that the Democratic nominee has been experiencing a cough related to allergies. On Friday, she was diagnosed with pneumonia and is now on antibiotics and advised to rest and modify her schedule, said Bardack.

"While at this morning's event, she became overheated and dehydrated. I have just examined her and she is now re-hydrated and recovering nicely," Bardack said in the statement. The campaign is reviewing whether to reschedule fundraising events in California on Monday and Tuesday.

The incident comes at an inopportune time for the Clinton campaign, which has been fighting Internet rumors about her health after a recent coughing spell which she laughed off by saying “Every time I think about (Donald) Trump I get allergic.”

In an Aug. 15 speech, her Republican challenger, Donald Trump, said Clinton “lacks the mental and physical stamina to take on ISIS, and all of the many adversaries we face.” And in a column in USA TODAY, former New York mayor Rudy Giuliani said there are unanswered questions about Clinton's health, although he added that "I hope Secretary Clinton is perfectly healthy."

There are also fake medical records circulating on conservative Internet websites and Fox News’ Sean Hannity recently played footage of Clinton vigorously shaking her head to avoid answering a question from her press corps that he said was “seizure-esque.” It prompted one of the reporters who witnessed the incident to publish a response knocking down the claim.

Yet the slow response of the campaign on Sunday — Clinton left behind her traveling press corps, which was not given an explanation until about 90 minutes after her disappearance from the event — contributed to speculation throughout the day about whether she had suffered a dizzy spell or something worse. The campaign was also criticized for not disclosing the pneumonia diagnosis at the time it was made.

A Twitter video posted under the account Zdenek Gazda showed a wobbly looking Clinton being helped into a van upon leaving the memorial service.

New York temperatures on Sunday were in the low 80s, with humidity in the mid-40s. The Democratic presidential nominee left her daughter Chelsea’s apartment shortly after 11:45 a.m., waving at people gathered on the sidewalks. Clinton also hugged and took a picture with a little girl who was allowed past the security line.

Doctor: Clinton left 9/11 event due to heat, pneumonia

Neither candidate has released a more complete medical report, though Trump recently told ABC News that he would do so.

In December, Dr. Harold Bornstein issued a one-page statement asserting that Trump would be “the healthiest individual ever elected to the presidency.”

At 70, Trump would be slightly older than Ronald Reagan on his election day, and Clinton will have just turned 69.

In July 2015, Bardack, an internist in Mount Kisco, N.Y., said Clinton is a “healthy 67-year-old female whose current medical conditions include hypothyroidism and seasonal pollen allergies.” She concluded that Clinton is in “excellent physical condition and fit to serve.”

Clinton’s letter of health was nearly two pages long and had standard lab results, while Trump’s was a few paragraphs with few details. In 2008, Republican Sen. John McCain released more than a thousand pages of medical records to show he was cancer-free and fit to serve as president.

Critics point to a 2012 concussion Clinton suffered after fainting and striking her head. Bardack said Clinton had a stomach virus after traveling and had become dehydrated.

Yet Clinton, who is now 68, also had to undergo anticoagulation therapy to dissolve a blood clot and had to wear special glasses to correct double vision for nearly two months starting in late 2012. Bardack said follow-up exams in 2013 “revealed complete resolution of the effects of the concussion as well as total dissolution of the thrombosis.”