WATCH: Clinton campaign says she left 9/11 event feeling overheated

NEW YORK — Hillary Clinton abruptly left Sunday's 9/11 anniversary ceremony in New York after feeling "overheated," according to her campaign, and retreated to her daughter's nearby apartment. As she exited the apartment shortly before noon, Clinton said, "I'm feeling great."

Clinton spokesman Nick Merrill said in a statement that the Democratic presidential nominee attended the morning ceremony for 90 minutes before departing. Merrill said Clinton was "feeling much better," but offered no additional details, including whether the 68-year-old Clinton required medical attention.

A senior law enforcement official who was briefed on the matter said that after leaving the memorial plaza, Clinton was observed "fainting" in a departure area. That official spoke on condition of anonymity, because he wasn't authorized to disclose information publicly.

Video taken at the scene and posted on social media shows Clinton being held up by three people. She staggers and appears to trip on a curb as they help her into a vehicle.

Clinton's departure from the event was not witnessed by the reporters who travel with her campaign, which did not offer any information about why she left and her whereabouts for more than an hour.

Clinton walked out of daughter Chelsea Clinton's apartment on her own and made only a brief comment to the reporters waiting outside, saying "It's a beautiful day in New York." She waved and posed for a photo with a young girl before getting into her motorcade.

The campaign also did not take reporters in the motorcade after Clinton's departure from her daughter's apartment. An aide said the former secretary of state was heading to her home in Chappaqua, New York.

The incident comes less than two months from Election Day and compounds an already difficult stretch for Clinton. Despite Trump's numerous missteps, the White House race remains close and the public continues to view Clinton has dishonest and untrustworthy.

On Friday, Clinton told donors that "half" of rival Donald Trump's supporters are in a "bucket of deplorables" — a comment that drew sharp criticism from Republicans. Clinton later said she regretted applying that description to "half" of Trump's backers, but stuck by her assertion that the GOP nominee has given a platform to "hateful views and voices."

For months, Trump's supporters have tried to make the case that Clinton is physically unfit for the White House, citing a concussion she sustained in December 2012 after fainting. Her doctor attributed that episode to a stomach virus and dehydration.

Clinton's doctor reported she is fully recovered from the concussion, which led to temporary double vision and discovery of a blood clot in a vein in the space between her brain and skull. Clinton also has experienced deep vein thrombosis, a clot usually in the leg, and takes the blood thinner Coumadin to prevent new clots.

Trump attended the same memorial service at ground zero in lower Manhattan, along with New York's Democratic senators, Chuck Schumer and Kirstin Gillibrand. The weather was warm and humid in New York on Sunday, and there was a breeze at the crowded memorial plaza during the ceremony.

Asked after the event about Clinton's health incident, Trump said, "I don't know anything about it."

Neither Trump nor Clinton spoke at the event, in keeping with the solemn nature of the annual remembrance of the deadliest terror attack on American soil.

Trump's personal physician has said the Republican presidential nominee is in excellent health both physically and mentally. But the 70-year-old has refused to release his own health records.

Dr. Harold Bornstein's report last December remains the only medical information released so far by the Trump campaign. Bornstein told NBC News he needed just five minutes to write a glowing public assessment of Trump's health as a limousine waited to carry the letter back to Trump.

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