NEW YORK — Hillary Clinton’s doctor said the Democratic presidential nominee was diagnosed on Friday with pneumonia, put on antibiotics and advised to rest and modify her campaign schedule.

Dr. Lisa Bardack said in a statement that Clinton is “recovering nicely” after attending a Sept. 11 anniversary event in lower Manhattan. Clinton was seen on video appearing to struggle to stay on her feet as she got into a vehicle to leave the event.

Bardack said Clinton has been experiencing a cough related to allergies, and in a follow-up examination of her cough on Friday, Clinton was diagnosed with pneumonia.

The statement said Clinton became overheated and dehydrated at the 9/11 event.

Clinton spokesman Nick Merrill said in a statement that the Democratic presidential nominee attended the morning ceremony for 90 minutes “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,” Merrill said.

The statement offered no additional details, including whether Clinton, 68, 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.

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.

Donald Trump supporters have tried to make the case that she’s 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.

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. The campaign also did not take reporters in the motorcade after Clinton’s departure from her daughter’s apartment, and it was unclear where she was headed from there.

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 Republican nominee 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.