US Republican presidential candidate Donald Trump has pledged to release details about his health after his Democratic rival Hillary Clinton was diagnosed with pneumonia.
Mr Trump said health had now become "an issue" in the election campaign.
Mrs Clinton was taken ill on Sunday at a 9/11 memorial ceremony and cancelled a campaign trip to California.
She will also be releasing new medical records to help ease concerns about her health, a campaign spokesman said.
"There's no other undisclosed condition. The pneumonia is the extent of it," Brian Fallon told MSNBC.
He said she would probably resume campaigning in the next few days.
Mrs Clinton said on Twitter she was "anxious" to return to the trail.
The incident capped off a difficult weekend for Mrs Clinton, who came under attack from Mr Trump for calling half of his supporters "deplorable" people on Friday.
Mr Trump wished her a speedy recovery and said he would release the results of a medical examination he took over the past week, with "very, very specific numbers".
"Hopefully they're going to be good. I think they're going to be good. I feel great," he told Fox News.
So far Mr Trump has only released a note, in which his doctor declared that he would be "the healthiest individual ever elected to the presidency".
Mr Trump, 70, and Mrs Clinton, 68, are among the oldest US presidential candidates in history.
White House spokesman Josh Earnest said it was "entirely legitimate" for Americans to want to know about the health of their president but that it was up to the candidates to decide what level of detail they were prepared to release.
On Sunday, video showed Mrs Clinton being supported by aides as she entered a van to leave the 9/11 ceremony after an hour and 30 minutes.
Her campaign initially said she had been taken to her daughter's New York flat after feeling "overheated".
She re-emerged later on Sunday, telling reporters: "I'm feeling great. It's a beautiful day in New York."
Doctors subsequently confirmed she had been diagnosed with pneumonia on Friday.
Some critics questioned why this had only been revealed after Sunday's events.
Mrs Clinton's communications director has admitted the campaign "could have done better" managing Sunday's incident.
The candidate had been due to leave for California on Monday morning for a two-day trip that included fundraisers, a speech on the economy, and an appearance on the Ellen DeGeneres Show.
She is now resting at home in Chappaqua, New York.
Mrs Clinton suffered a coughing fit last week at a campaign event in Cleveland, Ohio, which fuelled speculation about her condition.
Last month, her personal doctor Lisa Bardack said in a letter that the candidate was "in excellent health and fit to serve as president of the United States". She had made a full recovery from surgery she underwent in 2012 for a blood clot, the doctor added.
But Mr Trump has repeatedly suggested she is unfit, telling supporters last month she "lacks the mental and physical stamina" to serve as president.
"I don't know what's going on. I'm like you, I see what I see," he said after Mrs Clinton's pneumonia diagnosis was confirmed.
The Clinton campaign has accused opponents of pushing a "deranged conspiracy" about her health.
In other campaign developments:
- Donald Trump accused US Federal Reserve Chair Janet Yellen of keeping interest rates low to boost President Barack Obama's popularity. He said she should be "ashamed"
- The Republican candidate also released a new ad attacking Mrs Clinton for calling half of his supporters "a basket of deplorables" last week. "You know what's deplorable? Hillary Clinton viciously demonising hard-working people like you," a narrator says
- Green Party candidate Jill Stein says she would not have killed Osama Bin Laden but instead would have put him on trial
Major fall or just a stumble? - Anthony Zurcher, BBC News
Will Hillary Clinton's near collapse during Sunday's 9/11 memorial ceremonies make her health a political Achilles' heel?
What should be most concerning to the Clinton team is that the Trump campaign managed to hold its tongue as the news unfolded, probably sensing that the story was damaging enough on its own. In his first public comments on Monday morning, for instance, Mr Trump only said that he hoped Mrs Clinton made a full recovery.
Presidential campaigns go through great efforts to portray their candidate as healthy and full of vigour, while presidents who had health troubles concealed their weaknesses.
At 68, Mrs Clinton is particularly susceptible to concerns about her health (as is 70-year-old Mr Trump). She has the additional challenge of being the first female presidential nominee from a major political party - and may have to face biases within the electorate over whether a female candidate is sufficiently "strong", regardless of her age.
But if she returns to her normal campaign schedule without incident after a few days of recuperation, she will go a long way towards putting health concerns to bed.
What the US press said
Writing in the Washington Post, Todd C Frankel said Mrs Clinton had for years been discreet about her medical history and her discretion "made it difficult for voters to assess her complete health picture".
NBC News reporters said the incident had "sparked renewed calls for both Clinton and Trump, who are 68 and 70, respectively, to reveal more about their health".
Adam Nagourney, New York Times LA Bureau Chief, tweeted: "Is this hadn't happened, would Clinton campaign have announced pneumonia? One reason why Clinton/Trump should release medical records."
Vox News pointed out that the US has a rich history of presidential candidates being less than clear about their medical histories. "Looking back, we now know a number of past presidents and presidential candidates who have actually been much sicker than the public knew."
What is walking pneumonia?
Mrs Clinton's team say she is suffering with "walking pneumonia" - a less serious type of the lung infection which leaves patients feeling unwell but doesn't usually require bed rest or hospitalisation.
Pneumonia is essentially an infection of the lungs which causes inflammation in the air sacs and fills them with fluid. Symptoms can include a cough, fever, fatigue, chills and shortness of breath.
Anyone can contract pneumonia, although smokers, older people, and sufferers of chronic lung diseases are at increased risk. There are two types - bacterial or viral. Bacterial pneumonia is common and easily treated with antibiotics.
Most people with so-called "walking pneumonia" can recover within a few days. Those with weak immune systems or existing conditions can take weeks to recover, and pneumonia can in some cases be fatal.bb