BEIJING, Sept. 13 (Xinhua) — U.S. Democratic presidential nominee Hillary Clinton's health scare has triggered fresh speculation about her health and revived concerns about her physical fitness for running for the White House.

The former secretary of state on Sunday morning abruptly left a 9/11 memorial in New York and her campaign initially told reporters that Clinton had been "overheated."

Soon a video shot by a witness surfaced online, in which an apparently ailing Clinton struggled to steady herself and had to be helped by two secret service agents into her van. She was driven to her daughter's apartment in Manhattan.

About 90 minutes after the episode, Clinton emerged and waved to onlookers. As she came out of the apartment shortly before noon, Clinton said, "I'm feeling great. It's a beautiful day in New York." She was then driven to her home in suburban Chappaqua, New York.

Almost five hours after the release of the video, the Clinton campaign released a statement from Clinton's physician which read that Clinton had been diagnosed with pneumonia on Friday and left the memorial after becoming dehydrated and overheated.

The Democratic nominee said she did not disclose pneumonia diagnosis immediately because she did not "think it was going to be that big a deal."

"There's no other undisclosed condition. The pneumonia is the extent of it," Clinton spokesman Brian Fallon told MSNBC.

Her campaign acknowledged on Monday it mishandled public concerns about Clinton's medical condition and said additional medical details of Clinton's would soon be released.

In an unusually restrained manner, her rival, Republican presidential candidate Donald Trump, offered her his wishes for a rapid recovery in his first public comments since Clinton left Sunday's Ground Zero ceremony.

"Something is going on but I just hope she gets well and gets back on the trail, and we'll be seeing her at the debate" in two weeks, the Republican told Fox News.

But he also said Clinton's health issues were of longer standing than admitted, and promised to release "very, very specific numbers" from a medical exam he took last week.

Trump and his supporters have questioned Clinton's health, saying Clinton is physically unfit for the White House and accusing her of being "exhausted" and sleeping too much.

However, Trump, who shared even less information about his own medical details than Clinton did, was also bogged down in controversy surrounding his brief medical report that stated that Trump would be the "healthiest individual ever elected to the presidency."

It was later disclosed that the doctor who wrote the only public documentation about Trump's health spent five minutes writing the report.

Clinton's husband, former President Bill Clinton, said in an interview Tuesday with PBS that Hillary Clinton is "doing fine" after a good night's sleep. He added that if there are more health problems that caused her apparent weakness Monday, "then it's a mystery to me and all of her doctors."

He said that "on more than one occasion" over the years "the same sort of thing's happened to her when she got severely dehydrated."

According to an aide to the former president, Bill Clinton will fly to a campaign event Wednesday in Nevada on behalf of his wife, who was forced to cancel a series of campaign fundraisers in California scheduled on Monday and Tuesday.

Speculation about Clinton's health dates back to 2012, toward the end of her tenure as secretary of state.