Democratic presidential candidate Hillary Clinton is assisted as she leaves a memorial service on the 15th anniversary of the 9/11 attacks in New York City. (Zdenek Gazda)

Hillary Clinton’s campaign left reporters in the dark for a full 90 minutes about her health and whereabouts on Sunday after she unexpectedly left a 9/11 memorial event in New York. It took most of the day to disclose that Clinton was diagnosed with pneumonia nearly three days earlier and wasn’t simply “overheated,” as the campaign’s initial statement on Sunday said.

The campaign’s limited and confusing disclosures frustrated reporters who cover Clinton and seemed to play into health rumors that have been promoted by her Republican opponent, Donald Trump, and his surrogates and touted in conservative media outlets.

Pool reporters — those who follow the Democratic nominee into restricted spaces and provide reports to other reporters — never saw her leave the commemorative event at the World Trade Center complex in Lower Manhattan and then apparently collapse into a van. The pool was confined to a media pen out of sight of Clinton’s location. Footage of her halting departure was captured by a bystander, Zdenek Gazda, who noticed her being helped to the vehicle.

The news appears to have been broken Sunday morning on Twitter by Fox News reporter Rick Leventhal. Citing an unnamed source, Leventhal tweeted at 9:42 a.m. “Hillary Clinton ‘clearly having some medical episode’ & had to be helped into van by her protective detail at WTC.”

Shortly thereafter, Leventhal, citing a law enforcement source, tweeted that Clinton “appeared to faint on way into van” and that she “stumbled off curb, ‘knees buckled,” lost a shoe as she was helped into vans.” He said his source “watched it happen.”

Video of Clinton’s departure seemed to show her buckling and stumbling as she got into her van. (Thomas Johnson/The Washington Post)

Leventhal’s reporting was initially met with skepticism by people who suggested it might be a continuation of inflated claims about Clinton’s health pushed by Trump and conservative media sources, such as Breitbart News. But Leventhal’s reporting was accurate.

It wasn’t until about 90 minutes later that Clinton’s spokesman, Nick Merrill, released a statement saying that the candidate felt “overheated” and went to her daughter’s apartment in Manhattan. The statement made no mention of pneumonia.

Clinton emerged from Chelsea Clinton’s apartment around noon, telling reporters she was “feeling great” and that it was “a beautiful day in New York.”

She declined to speak further to the media and left for her home in suburban Chappaqua, N.Y. Her campaign offered no updates throughout the afternoon.

Clinton and her supporters have pushed back against opponents’ suggestions that she is hiding a health problem; Clinton’s personal doctor said last year that she is in “excellent physical condition” and “fit to serve” as president.

But the relative silence from the campaign about her condition Sunday may help propel doubts planted by her rivals, said Jane Hall, a communications professor at American University in Washington.

“I’m surprised they haven’t made some further statement about it,” said Hall, interviewed in late afternoon Sunday, before the pneumonia statement was released. “I can imagine they don’t want to play into conspiracy theories about her health, but if you don’t say something, if you’re not out there, pretty soon the silence begins to be interpreted in a negative way.”

Although he hasn't responded to Hillary Clinton's recent poor health at a memorial service and disclosure of a pneumonia diagnosis, Donald Trump and his campaign have repeatedly attacked her "strength" and "stamina" before. (Jenny Starrs,Bastien Inzaurralde/The Washington Post)

In fact, cable TV figures soon began speculating about what could have caused Clinton’s difficulties. On CNN, medical correspondent Sanjay Gupta raised a number of possibilities, from dehydration to adverse drug reactions (Clinton takes thyroid medication and blood thinners, and she treats allergies with antihistamines) to the aftereffects of a 2012 concussion. Gupta, a doctor, clearly labeled his observations “speculative,” and added, “At the very least, we’re owed an explanation.”

It wasn’t until around 5:20 p.m. that Clinton’s campaign issued a statement from her doctor, Lisa Bardack, saying that Clinton has been diagnosed with pneumonia on Friday and is “recovering nicely.”

The statement left a number of questions unaddressed: Why was the diagnosis withheld for nearly three days? Was the pneumonia related to Clinton’s coughing jag last week during a campaign event in Cleveland? Will her condition affect her campaign schedule, including a scheduled trip Monday to California?

It also seemed to contradict the campaign’s statement earlier in the day that Clinton had merely been “overheated” during the morning ceremony.

The lack of disclosure feeds another criticism about Clinton from Trump, noted Hall: That she is secretive and hides from the media.

“If she doesn’t want to fuel endless questions, she or her [campaign aides] have to get out there.”

Both presidential candidates have been sparing in their release of personal medical records, although Trump has been more withholding.