INDIANAPOLIS -- Gov. Frank O'Bannon was in critical condition at a Chicago hospital Monday afternoon after undergoing surgery for a cerebral hemorrhage, which was discovered after he was found unconscious in a hotel room there earlier in the day.
A doctor at Northwestern Memorial Hospital said bleeding on O'Bannon's right side of his brain may have been caused by a stroke.
In addition, some type of trauma caused more bleeding on both sides of the brain, indicating he may have fallen, said Dr. Wesley Yapor, a neurosurgeon in charge of O'Bannon's surgery.
Yapor said the surgery to remove blood from the brain went "very well," but O'Bannon's chances of recovery weren't immediately known. Yapor said the next 24 to 48 hours would be critical for the governor.
Without the surgery, the governor would not have survived, Yapor said. O'Bannon was in a drug-induced coma after the operation.
O'Bannon was found unconscious around 9 a.m. in his room at the Palmer House Hilton in downtown Chicago, where he was planning to speak at a meeting of the Midwest U.S.-Japan Association, officials said.

The governor was admitted to the hospital around 9:30 a.m. He was unconscious and unresponsive from the time he was found, though he was breathing on his own at the hotel, a Northwestern Memorial Hospital doctor said.
O'Bannon was found in the hotel room after his staff members weren't able to reach him by phone, officials said.
O'Bannon's press secretary, Mary Dieter, said O'Bannon's wife, Judy O'Bannon, had arrived at the hospital and was "holding up well." O'Bannon's daughter, Jennifer, was also at the hospital. His other adult children were en route.
Lt. Gov. Joe Kernan, who also was in Chicago for the conference, flew back to Indianapolis after O'Bannon was taken to the hospital and told reporters he was
assuming acting-governor duties.
A formal, temporary transfer of power as allowed in Indiana's constitution wasn't done Monday. Kernan (pictured, left) said everyone involved agreed it was too soon to use the constitutional process without more information.
O'Bannon, a Democrat, is in the third year of a second four-year term. By law, he cannot seek re-election.

O'Bannon suffers from familial tremors, a neurologic disorder that involves involuntary shaking, RTV6 reported. The condition typically gets worse when the affected person tries to move or become more active. The condition is not considered life-threatening.
"As far as we know, he has had excellent health. He has had annual physicals ... for a man of his age, he has been reported to be in excellent health each time he's had a physical," O'Bannon spokesman Andrew Stoner said.
Dieter said O'Bannon was given a clean bill of health when he had his last physical three months ago.
O'Bannon was scheduled to be in Chicago only for a couple of days, RTV6's Norman Cox reported. He had been on vacation in his hometown of Corydon, Ind., before going to the conference.
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