Less than two months before the 2016 presidential election, health has become a genuine issue in the race.

Hillary Clinton's campaign announced Sunday night that she is canceling several upcoming events in the wake of her apparent collapse at a 9/11 memorial and a diagnosis of pneumonia.

Donald Trump promised Monday morning to release "very, very specific" results of a full medical exam that he recently had.

"This last week, I took a physical, and I'll be releasing when the numbers come in," Trump told Fox News.

Trump and his camp said Clinton's diagnosis proves that her health is a big issue for the campaign. He has been calling attention to her recurring cough and physical fitness for weeks.

But how much does the public need to know about a presidential candidate's health?

In the past, most candidates have kept their medical histories to themselves. Only a few have released detailed medical records, like John McCain did in both 2000 and 2008.

But if a nominee is dealing with a serious illness, many argue that the American people have a right to know about it.

"It's a controversial issue because some illness can be blown out of proportion and with modern medicine, a person can do well. But if a person is suffering from early Alzheimer's or another serious disease, it's quite another story," Jerrold Post, author of "When Illness Strikes the Leader," told CNN.

There have been candidates who managed to keep serious ailments under wraps.

Rumors about Franklin D. Roosevelt's  failing health surrounded his final presidential campaign in 1944, but most people didn't know the extent of his ailments until he died the next year.

Clinton has refused to release any detailed medical records thus far, but many are speculating that she'll address the issue soon.