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 at the weekend.
"I felt dizzy and I did lose my balance for a minute, but once I got in (the van), once I could sit down, once I could cool off, once I had some water, I immediately started feeling better," Clinton told CNN, adding that she would be back on 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.
The campaign said she "felt overheated," then released a statement by her personal doctor, Lisa Bardack, revealing that Clinton had been diagnosed with pneumonia Friday and was suffering from dehydration.
"There's no other undisclosed condition. The pneumonia is the extent of it," Clinton spokesman Brian Fallon told MSNBC.
Clinton was forced to scrap her California fundraising trip Monday and Tuesday. And the campaign acknowledged, just as Clinton was tweeting, that she will not attend her scheduled campaign event Wednesday in Nevada -- with Bill Clinton due to stump there on her behalf according to an aide to the former president.
In his first public comments since Clinton abruptly left Sunday's Ground Zero ceremony, an unusually subdued 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.
ANOTHER ANGLE OF #CLINTONCOLLAPSE WOW. pic.twitter.com/jqOpP11omI — Stefan Molyneux (@StefanMolyneux) September 11, 2016
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, on Twitter.
Fallon admitted: "I think in retrospect we could have handled it better in terms of providing more information more quickly."
'Not the first time'
The episode has fuelled fresh speculation and conspiracy theories on the internet, already awash with unsubstantiated rumors Clinton may have a brain tumor, Parkinson's or dementia. #HillarysBodyDouble was trending on Twitter Monday.
The root of persistent claims about Clinton's health lies in 2012, towards 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 assured 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."
The former first lady has dismissed rumors about her health, but Trump has repeatedly raised doubts about Clinton's stamina and physical strength, and on Monday 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.
Trump told Fox News he had a physical last week and would release "very, very specific numbers" once test results are back.
'Hard time keeping up'
Clinton was resting at home on doctor's orders on Monday, and phoning into a fundraising event in San Francisco, said spokesman Nick Merrill.
Her 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.
Asked for Obama's thoughts about Clinton being sidelined by illness, White House spokesman Joshua Earnest said "it certainly does not impact his assessment that she is the best person in the country to succeed him."
Trump meanwhile continued to assail Clinton for recently criticizing half of his supporters as a "basket of deplorables."
"If Hillary Clinton will not retract her comments in full, I don't see how she can credibly campaign any further," Trump told supporters in Baltimore.
