Clinton said in the live telephone interview with CNN that she started to feel hot at the event, which took place on a muggy day in New York. There was little shade where Clinton was standing alongside other dignitaries.

As family members of 9/11 victims read the names of the nearly 3,000 people killed in the attacks, she decided to leave and get a drink of water. She was wearing a wool suit and had been diagnosed with pneumonia on Friday, a fact her campaign had not made public.

In fact, campaign aides said Monday, a number of staff members at her campaign headquarters had been ill in recent weeks, including campaign manager Robby Mook.

At the apartment, she played with her grandchildren, even chasing them around the room, Fallon said. Clinton exited the building on her own, wearing sunglasses and carrying a handbag.

She waved to reporters and said: “I’m feeling great. It’s a beautiful day in New York.” She was then driven to her home in suburban Chappaqua, New York.

The public was left in the dark about Clinton’s whereabouts for about 90 minutes, sparking widespread speculation about her condition. That was a mistake, Fallon said.