Hillary Clinton sought to draw a line under the health scare rocking her White House campaign, assuring supporters she will return to the fray this week.
Clinton was set to get a boost Tuesday, when President Barack Obama hits the campaign trail in Philadelphia to support her bid to replace him.
Her husband, former president Bill Clinton, will campaign for her in Las Vegas on Wednesday.
Facing intensifying scrutiny about her health, the Democrat will also make new disclosures of medical records and data, as her team acknowledged it stumbled when it failed to transparently alert the press and public about Clinton's condition over the weekend.
"I just didn't think it was going to be that big a deal," Clinton told CNN when asked why she kept her pneumonia diagnosis on Friday under wraps until Sunday.
"It's just the kind of thing that if it happens to you and you're a busy, active person, you keep moving forward."
Discussing the event itself, she explained: "I felt dizzy and I did lose my balance for a minute. Clinton vowed to return to the campaign trail within the "next couple of days."
Clinton, 68, fell ill at a 9/11 memorial event in New York and was seen wobbling as she was helped into her vehicle, forcing her campaign to disclose she had been diagnosed with the acute respiratory infection.
The incident -- captured on amateur video -- gave her Republican rival Donald Trump, 70, a new opening to question her fitness for the nation's highest office as the race heats up with eight weeks until Election Day.
"There's no other undisclosed condition. The pneumonia is the extent of it," Clinton spokesman Brian Fallon told MSNBC.
On CNN, Clinton initially said that she has "twice" gotten dehydrated and felt dizzy over the past five years, then said it had been "a few times."
- Scuttled travel plans -
Her health woes forced Clinton to scrap her California fundraising trip Monday and Tuesday and a scheduled campaign event Wednesday in Nevada.
In his first public comments since Clinton abruptly left Sunday's Ground Zero ceremony, an unusually restrained Trump offered her his wishes for a rapid recovery.
But he also suggested the former secretary of state's health issues were of longer standing than admitted.
"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.
The unexpected turn of events has turned a conservative angle of attack into a serious line of questioning about Clinton's health and why it took two days to reveal the pneumonia diagnosis.
"Antibiotics can take care of pneumonia. What's the cure for an unhealthy penchant for privacy that repeatedly creates unnecessary problems?" asked David Axelrod, a former White House aide to Barack Obama.
Clinton admitted: "If we weren't fast enough, you know, I've talked to my staff, we, you know, take responsibility for that."
But she quickly insisted she has been far more transparent than Trump.
"The information is out there. You can't say the same thing about Donald Trump," she said.
"The American people deserve to know what he's up to and what he is hiding."
- 'Not the first time' -
The episode has fueled fresh speculation and conspiracy theories on the internet, already awash with unsubstantiated rumors Clinton may have a brain tumor, Parkinson's or dementia.
The root of persistent claims about Clinton's health lies in 2012, toward the end of her tenure as secretary of state.
A stomach virus and dehydration prompted her to faint, causing what her doctor said was a concussion.
Doctors said they found a blood clot on the brain.
Clinton later received the all-clear.
On Monday, Fallon insisted that "there was nothing here in terms of anything that was caused by what happened in 2012."
He also said Clinton's team would be releasing medical records "in the next few days" in order to "further put to rest any lingering concerns about what you saw yesterday."
Trump also promised to release medical records once test results are back.
The former first lady has dismissed rumors about her health, but Trump has repeatedly raised doubts about Clinton's stamina and physical strength, and he questioned her campaign's account of the current episode.
"They say pneumonia on Friday, but she was coughing very, very badly a week ago and even before that if you remember, and this was not the first time," he told CNBC.
Clinton spokesman Fallon said several senior Clinton collaborators at campaign headquarters in Brooklyn also fell ill in recent weeks, including campaign manager Robby Mook. But it was not known if that was the source of Clinton's infection.
Democrats including her running mate Tim Kaine rushed to her defense.
"Her energy staggers me," he told a crowd in Dayton, Ohio. "I have a hard time keeping up with her."