Hillary Clinton is sick. And sick happens. If there's one thing that ails her campaign, though, it might not be the Democratic presidential nominee's newly announced bout of pneumonia. It might be a built-up resistance to transparency.

Clinton's doctor revealed on Sunday she is taking antibiotics for a mild form of the common bacterial infection, following the 68-year-old former secretary of state's hasty departure from a Sept. 11 memorial service in New York.

A campaign statement said Clinton felt "overheated" about 90 minutes into the ceremony. Around 9:30 a.m., her security detail took her to her daughter's New York City apartment to rest and rehydrate. It was more than six hours later that reporters learned of her pneumonia. By that time, footage of a wobbly-looking Clinton swooning near a motorcade had already begun to kick up clouds of conjecture about a fainting spell and something more serious.

Clinton's pneumonia diagnosis left a lot of air time to fill with speculation and condemnation, CBC's Lyndsay Duncombe reports 2:42

Damning as the optics are, so is the timing. Clinton's physician, Dr. Lisa Bardack, diagnosed her on Friday — a fact the campaign only made known two days later, after rumours fanned out about her abrupt exit on Sunday.

There was disclosure, yes. But possibly a forced one, coming about two weeks from the first debate of the general election on Sept. 26.

Clinton said Monday she didn't think her pneumonia diagnosis was significant enough to disclose beforehand.

"I just didn't think it was going to be that big a deal," she told CNN, adding she thought she could "just keep going forward and power through it, and that didn't work out so well."

Either way, the episode underscores the perils of the "inclination towards secrecy" that has coloured Clinton's campaign, says Kyle Kondik, managing editor of the University of Virginia's political newsletter Sabato's Crystal Ball.

Delayed revelation

The delayed revelation comes amid a monsoon of conservative-fuelled conspiracy theory regarding Clinton's health. For a period of time on Sunday, her whereabouts were unknown.

Hillary Clinton 9/11 NYC <a href="https://t.co/q9YnsjTxss">pic.twitter.com/q9YnsjTxss</a> —@zgazda66

"And when people don't know what's going on with a candidate, there's an information vacuum that leads to speculation," Kondik says.

David Axelrod, President Barack Obama's former chief campaign strategist, tweeted on Monday morning that while pneumonia can be knocked out with antibiotics, the more serious affliction plaguing Team Hillary remains "an unhealthy penchant for privacy that repeatedly creates unnecessary problems."

When a candidate has to change a schedule due to unusual circumstances, "you just need to fess up right away," Axelrod said on CNN.

Antibiotics can take care of pneumonia. What's the cure for an unhealthy penchant for privacy that repeatedly creates unnecessary problems? —@davidaxelrod

Secrecy has been a malady afflicting both candidates. Clinton's run has been beset with trust issues, many stemming from her use of private email servers as secretary of state. Her Republican rival Donald Trump has refused to release his 2015 income tax returns, as Clinton and her running mate Tim Kaine did last month.

Clinton, who has declined to release detailed medical records, will release more documents. Trump pledged on Monday he would provide "very specific" results from a recent physical exam on The Dr. Oz Show. In a break from tradition, neither Clinton nor Trump have permitted a full "protective pool" of reporters to follow them for minute-to-minute coverage.

Hillary Clinton attended the Sept. 11 commemoration ceremony with New York Mayor Bill de Blasio. (Justin Sullivan/Getty Images)

That lack of a travelling press corps stirred up confusion on Sunday, when Clinton left the Sept. 11 memorial early and without immediate explanation. Only a 19-second online video provided any clues, leaving social media commenters to flesh out a missing narrative. Silence from the Clinton camp did nothing to control hearsay.

Information about her whereabouts finally came out at 11 a.m. In the meantime, there was a 90-minute void in which journalists pursuing confirmation of any details of a possible health emergency, reportedly visited area hospitals, arguably making an unfortunate situation worse.

"The more uncertainty there seems to be, the more it may feed into a lot of those conspiracy theories," Kondik says. "And it's a lot of unfounded stuff."

The diagnosis of pneumonia should not itself pose an immediate medical concern.

Mike Czin, who served as the Obama for America campaign spokesman in 2012, also came down with what's often referred to as walking pneumonia during that primary race.

"It's not uncommon. It sucked. I was coughing this awful hollow, dry cough. But things happen on presidential campaigns," says Czin, now the vice-president of the political consulting firm SKDKnickerbocker in Washington. "They gave me an inhaler and some antibiotics and it started to clear up pretty quickly."

'A germ-contact sport'

Dave Wade, the former chief of staff to Secretary of State John Kerry, notes that Kerry also battled through walking pneumonia during his run in the 2004 primaries, as well as a broken collarbone from a cycling mishap.

"We never felt compelled to alert the media because it would've distracted from our message," Wade says.

"Running for president is a germ-contact sport. Candidates spend all day shaking thousands of hands on rope lines then flying millions of miles in Petri dish planes full of recycled air. They're up all night and rise at the crack of dawn. They get sick."

Although it has been tradition for both candidates to release medical records, Wade believes a reciprocal approach is the way to go. By no means should Clinton be the only candidate held to a standard, he says.

Trump's four-paragraph assessment by gastroenterologist Harold Bornstein was met with ridicule for its bizarrely worded statement describing him as having "astonishingly excellent" lab test results and "extraordinary" strength and stamina.

Hillary Clinton left the Sept. 11 commemoration ceremony early. Her doctor later said she had been diagnosed with pneumonia on Friday. (Justin Sullivan/Getty Images)

And yet, "we're now entering a cable television debate about whether the campaign with a secrecy problem is the Clinton campaign," Wade says. "If the issue is going to be secrecy, Trump's the wrong candidate to carry that message."

Trump has, for the most part, resisted commenting about the medical situation, beyond wishing her a speedy recovery.

New York Trump surrogate Joe Borelli also stuck to the message, though the Staten Island Republican councilman said he foresees Clinton's health becoming "a significant issue if the health issue keeps her from campaigning."

"We wish her well," Borelli adds. "We'd like to see her have a recovery, and we'd rather beat her fair and square."

I'm actually pretty hyped for the Trump to release more medical stuff, but only because I've missed Dr Bornstein. <a href="https://t.co/fAYCmFIB4w">pic.twitter.com/fAYCmFIB4w</a> —@dr_nic

Democratic strategist Hank Sheinkopf questions whether scrutiny of Clinton's physical fitness for office plays into stereotypes of women as "weak" or somehow lacking the stamina to be commander-in-chief.

"Does it have to be a longstanding issue? If she gets back to the campaign trail quickly, it has limited value," he says. "The only way to deal with this, probably, would be to issue a health report by an independent doctor. Call it for what it is. Disclose and show you have nothing to hide."

Like anyone who’s ever been home sick from work, I’m just anxious to get back out there. See you on the trail soon. -H —@HillaryClinton

Clinton, who cancelled her West Coast trips for Monday and Tuesday, tweeted on Monday afternoon that she is "feeling fine" and ready to rejoin the campaign trail.

"Like anyone who's ever been home sick from work, I'm just anxious to get back out there."