Hillary Clinton´s presidential campaign suffered a fresh blow Sunday when the Democratic nominee fell ill and had to leave a 9/11 memorial ceremony in New York, an episode sure to fuel Donald Trump´s insinuations that she is not healthy enough to lead.

Clinton had been seeking to bounce back from a blunder on Friday, when she told donors that half of Trump´s supporters belonged in a "basket of deplorables" -- a comment she later had to walk back -- so Sunday´s incident was certainly ill-timed.

The former secretary of state was at the high-profile ceremony at Ground Zero in Manhattan for 90 minutes and greeted some family members of those killed in the deadly terror strikes 15 years ago, her campaign said in a statement.

"During the ceremony, she felt overheated so departed to go to her daughter´s apartment, and is feeling much better," the statement said.

A video posted on Twitter showed Clinton, wearing a blue suit and white blouse, seeming unsteady as she waited to get into a black van to leave the emotional 9/11 service.

She appeared to stumble as she was helped into the vehicle, and had to be held up on either side by members of her entourage.

It was a humid day in New York, with temperatures around 82 degrees Fahrenheit (28 Celsius).

"I didn´t see anything unusual. What I can tell you is that many of us (had) a sigh of relief when a gust of wind would come by because it was incredibly stifling," Democratic US Congressman Joe Crowley, who stood near Clinton for about an hour at the ceremony, told MSNBC.

Clinton reappeared a few hours later, apparently recovered as she walked out of her daughter Chelsea´s home. She smiled for the media and posed for pictures with a young girl before departing in a vehicle for her home in Chappaqua.

"I´m feeling great, it´s a beautiful day in New York," Clinton said.

Health issues?

Trump -- who also attended the 9/11 ceremony -- was uncharacteristically silent on Twitter about Clinton´s illness, as both candidates took a break from formal campaigning to mark the somber day of remembrance.

But the businessman, his spokespeople and surrogates have promoted the idea in recent weeks that Clinton, 68, has serious health problems.

The internet is awash with claims that she may have a brain tumor, Parkinson´s or dementia. Some complain she has "seizure-like facial expressions."

Trump, 70, has said Clinton is "not strong enough to be president" and that she "lacks the mental and physical stamina to take on ISIS."

Former New York mayor Rudy Giuliani, a Trump supporter, has said that Clinton "looked sick."

The root of the claims lies in 2012, when Clinton was nearing the end of her stint as secretary of state and a stomach virus and dehydration prompted her to faint, causing what her doctor said was a concussion.

They said they found a blood clot on the brain and Clinton temporarily suffered from double vision. She was later given the all-clear.

The former first lady has dismissed "conspiracy theories" about her health and points to a letter from her doctor declaring her fit to serve as president.

She blamed a coughing fit during a speech in Cleveland last week on allergies.

´Vitality and viability´

Clinton´s illness is unlikely to be a turning point in the White House race, said Jennifer Lawless, a professor of government at American University in Washington.

From all indications, it appears to just be a brief bout of overheating, she told AFP.

"What the Clinton campaign needs to do over the course of the next several days is demonstrate her vitality and viability. She has to be at tons of events and seem very energetic," Lawless said.

Larry Sabato, a veteran political scientist at the University of Virginia, said Clinton´s team needs to release a full health record to put the story to rest.

"We really haven´t gotten very much, essentially a letter from her doctor," he told CNN, but added that Trump should be held to the same requirement.

Clinton´s physician gave an overview of her medical history, including regular medications and results of routine screenings.

So far, Trump has only released a brief letter from his physician that was light on details but said if elected, he would be "the healthiest individual ever elected to the presidency."

Clinton´s illness struck less than two days after she told a crowd at a fundraiser that "to be grossly generalistic, you could put half of Trump´s supporters into what I call the basket of deplorables."

"The racist, sexist, homophobic, xenophobic, Islamophobic -- you name it."

Trump and his supporters slammed the remarks. Clinton said she regretted saying "half," but then listed a number of "deplorable" things about Trump.

"I won´t stop calling out bigotry and racist rhetoric in this campaign," she said.

A Washington Post-ABC News poll out Sunday -- conducted in the days before she made the remark -- shows that 70 percent of the electorate has already decided who to vote for. Only 30 percent are undecided or could switch.

Clinton leads Trump 46 percent to 41 percent among likely voters, according to the poll, which had a 4.5 percentage-point margin of error