Hillary Clinton says she is "feeling fine and getting better," as she recovers from pneumonia at her home in Chappaqua, outside New York City.
"Like anyone who's ever been home sick from work, I'm anxious to get back out there. See you on the [campaign] trail soon," Clinton tweeted.
Clinton's doctor diagnosed her with pneumonia on Friday.
She told CNN Monday that she ignored her doctor's advice to take it easy because she said she was "incredibly committed" to being at a September 11 anniversary event in New York City Sunday.
Clinton said she thought she could "power through" the event, but got overheated and had to leave early.
Video showed her nearly collapsing while being helped into her car. Her knees appeared to buckle under her.
Aides drove her to her daughter Chelsea's New York apartment, where she emerged several hours later, looking bright and telling reporters she felt great.
Clinton officials canceled campaign appearances Monday and Tuesday in California. She is under a doctor's orders to modify her schedule and get some rest.
Clinton Monday thanked everyone who sent their best wishes, which included Republican rival Donald Trump.
"I hope she gets well and gets back on the trail and we'll be seeing her in the debate," Trump said Monday, looking forward to their first face-to-face meeting September 26.
Campaign officials first said Clinton was overheated and dehydrated before admitting she had pneumonia.
"I think in retrospect, we could have handled it better in terms of providing more information more quickly," Clinton spokesman Brian Fallon told MSNBC television Monday when asked why it took so long to disclose her illness.
Fallon said there are no other hidden conditions. "The pneumonia is the extent of it."
Trump Continues Attacks
Trump did not let up on Clinton during a campaign stop in Asheville, North Carolina Monday, despite her health scare.
He attacked what he called Clinton's "Wall Street" agenda, saying she has "hate in her heart" for middle class Americans and looks down on people.
Clinton is 68 and Trump is 70. They are two of the oldest candidates to try to win the White House.
Some political analysts say both should release more information about their medical history.
Trump said he plans to release the results of a physical exam he had during the past week, with "very, very specific numbers." He has accused Clinton of not having the energy and stamina it takes to be president.
Some Trump supporters have suggested that she is seriously ill from the effects of a concussion she suffered in a fall in 2012.
Doctors said at the time she had a blood clot on her brain and temporarily suffered from double vision, before declaring her fully recovered.
Last year, Trump released a letter from a physician claiming he would be "the healthiest individual ever elected to the presidency."
The doctor, however, has since acknowledged that he dashed off the note in five minutes while a Trump campaign limousine waited nearby.