Sen. Tim Johnson, D-South Dakota, was hospitalized Wednesday after he suffered stroke-like symptoms in his Washington office, his staff said.
Johnson, who turns 60 on December 28, was taken to George Washington University Hospital by ambulance about 11:30 a.m., sources in his office said.
A statement issued by Johnson's office said he was suffering from a "possible stroke." But a spokeswoman later said that tests showed Johnson had suffered neither a stroke nor a heart attack, although it was not clear what had happened. (Listen to Johnson's difficulty speaking during a WNAX radio interview [MP3, 749 kb] -- :38)
Julianne Fisher, a spokeswoman for Johnson, told CNN he was still undergoing tests and will stay hospitalized overnight, but she would not characterize his condition.
"We're taking one day at a time," Fisher said, "saying a lot of prayers and waiting until morning."
Staff members said that Johnson was conscious when he was taken to the hospital.