"He felt uncomfortable," said aide Calvin McDowell. "That's what prompted him to come to the hospital."
Ford, 87, was among three former presidents honored during the second night of the convention.
John Van Fossen, a legislative aide for U.S. Rep. Pete Hoekstra, said the Michigan delegation was told that Ford was suffering from bronchitis.
Ford told CNN's Larry King, in an interview broadcast Tuesday night, that he's "looking forward" to living longer.
I couldn't be healthier," he said. "Betty and I are having a magnificent life: 52 years of married life, four great children, 15 grandchildren. Everything is breaking just right and I am delighted to be here at this convention after going to so many for so many years."
At Tuesday night's convention session, Ford sat beside and was honored along with former Republican Presidents George Bush and Ronald Reagan for his role in the country's, and the GOP's, success.
Earlier in the day, appearing on C-SPAN, he answered questions from a variety of callers on everything from the U.S. policy on Iran to whether President Clinton should be pardoned for any charges he might face.
Ford, frail but congenial, answered virtually all of the questions with detail and acuity.
Ford, the 38th and only unelected president in America's history, took office minutes after Nixon flew off into exile and declared "our long national nightmare is over."
But he revived the debate a month later by granting Nixon a pardon for all crimes he committed as president. That single act, it was widely believed, cost Ford election to a term of his own in 1976. He was in the White House only 895 days.
Ford also earned a place in the history books as the first unelected vice president, chosen by Nixon to replace Spiro Agnew who also was forced from office by scandal.
In a long congressional career in which he rose to be House Republican leader, Ford lit few fires. In the words of Congressional Quarterly, he "built a reputation for being solid, dependable and loyal - a man more comfortable carrying out the programs of others than in initiating things on his own."
When Agnew resigned in a bribery scandal in October 1973, Ford was one of four finalists to succeed him. Nixon picked Ford , saying he had known the congressman "longer and better than any of the rest." On Aug. 9, 1974, after seeing Nixon off to exile, Ford assumed the office.
After leaving the White House, he took up residence in the plush resort area of Palm Springs, Calif., picked up $1 million for his memoir and another $1 million in a five-year NBC television contract, and served on a number of corporate boards. By 1987, he was on eight such boards, at fees up to $30,000 a year, an was consulting for others, at fees up to $100,000. After criticism, he cut back on such activity.