Democratic presidential candidate Hillary Clinton has suffered from bouts of dehydration in the past, according to her husband and former US President Bill Clinton. The remarks relate to her pneumonia diagnosis that caused her to leave a 9/11 ceremony in New York City on Sunday.

"Rarely, on more than one occasion, over the last many, many years, the same sort of thing's happened to her when she got severely dehydrated, and she's worked like a demon, as you know, as secretary of state, as a senator, and in the years since," said Bill Clinton in an interview on CBS, reported by CNN.

Hillary Clinton spoke with CNN's Anderson Cooper on her dehydration episodes, noting that they happened "really only twice that I can recall," in an apparent response to rumors that she's in bad shape for the presidency.

"What happened yesterday was that I just was incredibly committed to being at the memorial - as a senator on 9/11, this is incredibly personal to me," Hillary Clinton said on her fainting spell as she left Ground Zero in New York City on Sunday.

Bill Clinton gave positive updates on his wife's condition, saying that she's "doing fine" at their New York home. "She was even better last night before she went to sleep. She had a good night's sleep. She just got dehydrated yesterday," said the former President.

Despite Hillary Clinton's age - at 68, she can become one of the US' oldest first-term Presidents, Bill Clinton said that she's more than capable to handle the presidency. He denied rumors that his wife is suffering from a medical condition more serious than pneumonia.

"Well, if it is (more serious) then it's a mystery to me and all of her doctors," said Bill Clinton. He added that "[Hillary Clinton] had two-and-a-half hard days before the day when she got dizzy," he said. "Today she made a decision, which I think was correct, to cancel her campaign day to take one more day to rest."