Dec. 20, 2007 -- DES MOINES, Iowa -- Former New York Mayor Rudy Giuliani was all smiles for the cameras as he left Barnes Jewish Hospital in St. Louis Thursday afternoon after experiencing headache pains so severe he had his charter plane turn around on the way from Missouri to New York and was rushed to the emergency room.
"I feel fine," Giuliani said, refusing to answer any reporters' questions as he left the hospital. His campaign released a statement from communications director Katie Levinson saying he was leaving the hospital after staying overnight with "a clean bill of health. Doctors performed a series of precautionary tests and the results of all the tests were normal."
The campaign shared no concrete medical information about which tests the mayor undertook and what the exact results were, also refraining from allowing the media to see his medical records or speak to his doctors.
In New York, his wife, Judith, told reporters that her husband is "in very good health," and gave a statement, but did not answer any questions.
Flying back to New York after a Chesterfield, Mo., fundraiser Wednesday night, Giuliani, who had been feeling sick and dizzy all day, told the pilot of his charter plane to turn around.
"The decision was made Wednesday night when he had a severe headache and fluike symptoms on his way home from Missouri to land the plane," Judith said. "EMS then performed a small evaluation and decided that for precautionary measures they would take him to Barnes Jewish Hospital."
Speculating on the case, Dr. William Schaffner, the chair of Preventive Medicine at Vanderbilt Medical Center told ABC News that "a severe headache is always a cautionary symptom. We take that very, very seriously. It could be anything. And nothing."
A senior Giuliani campaign official tells ABC News, "He's fine. He campaigns very vigorously. He did 77 events in 53 cities this month. He just got sick."
The presidential candidate's wife said that she "spent most of the night on the telephone with the doctors and the wonderful nurses at Barnes Jewish Hospital. They assured me that Rudy is in very good health."
After flying to New York Thursday afternoon, Giuliani was scheduled to visit with his personal physician.
From the lymphoma of former Massachusetts senator Paul Tsongas or the irregular heart rhythm of former New Jersey Sen. Bill Bradley, every medical issue takes on greater consequence in the harsh glare of the presidential stage.
The incident is also a painful reminder of the medical condition that forced Giuliani out of another political race almost eight years ago. Giuliani quit his Senate race against Hillary Clinton because of prostate cancer.
Campaign aides say Giuliani plans to return to the campaign trail as soon as Saturday. They are unapologetic about how little medical information they've provided to the public about the mayor's condition, despite his pledge of transparency at the last presidential debate in Iowa just last week.
"I would make sure that government was transparent," Giuliani said. "My government in New York City was so transparent that they knew every single thing I did almost every time I did it."
Jan Simmons, Avery Miller, Lisa Chinn and Richard Coolidge contributed to this report.