George Washington, the first President of the United States - and the first to be temporarily disabled while in office.

May 1790

Just a year into his first term - the first presidential term in United States history - George Washington contracts a severe case of influenza.  While contemporary accounts describe his condition as "near death," by any account the President isn't up to his job for a period of several weeks.  But in part because there's no clear mechanism in place, in part because the nation was less than a decade removed from the American Revolution, and in no small part because public perception might see it as a de facto coup d'etat, nothing happens.

Though a temporary transfer of executive authority would be in the best interests of the nation, Vice President John Adams would prove even more powerless than the laid up Commander-in-Chief.  Ultimately Washington recovers from his illness, but just as his retirement after two terms of service would establish the "two term" precedent, his 1790 would establish one as well:  a precedent in which a presidential disability would go unaddressed.  And while the two term precedent would end in 1941, the disability precedent would last 197 years.

June 1813

The man credited as the primary architect of the United States Constitution and the nation's fourth President, James Madison, is in trouble.  The fledgling country is fighting for its very survival against its former colonial masters in the War of 1812, and it's going badly.  The British Navy has effectively blockaded the eastern seaboard, Fort Erie keeps falling into enemy hands, Detroit is under siege, and the tactics that will ultimately result in the British raiding Washington, D.C., and setting fire to the White House are taking a toll on the Commander-in-Chief.

James Madison, fourth President of the United States and the "Father of the Constitution."

Suffering from what at the time were thought to be epileptic seizures but which in modern parlance would be best described as paralyzing panic attacks, the "Father of the Constitution" contracts malaria in June, 1813, adding delirium and a high fever to the mix.  Under these conditions Madison's in no condition to serve as President in peacetime, let alone in time of war.  But no serious discussion takes place regarding the prospect of Vice President Elbridge Gerry stepping in, even on a temporary basis.  The reason?  Gerry is in worse shape than Madison:  69 years old (comparatively ancient in that era) and suffering from the ailments that ultimately caused his demise 15 months later.  Madison would recover over the course of the next month.

Postscript

Five years later Madison's successor, James Monroe, would fall victim to malaria as well.  Like Madison, Monroe would fully recover and serve two full terms as President.  But like Madison, during his illness a transfer of executive authority during his illness was never contemplated.  In Monroe's case is was at least in part due to his Vice President, Daniel Tompkins, who was a non-functioning alcoholic, unfit to serve even temporarily as the nation's chief magistrate.  Just 99 days after leaving the Vice Presidency, Tompkins would suffer an alcohol-related death.