WASHINGTON - Sen. Harry Reid, D-Nev., was hospitalized today after he reported feeling sick, but his office says medical tests appear to give him a clean bill of health.

"Early this morning, Sen. Reid was not feeling well and as a precaution decided to go to the hospital," a news release from the majority leader's office reads. "Tests have been conducted, and everything is normal. He is alert, resting and feeling better. Doctors have asked that he remain in the hospital for observation, so he will not be working today."

A top Democratic aide tells ABC News that Reid is talking to his wife, a few senators and senior staff this morning by phone. They say he is expected to be released later today but will be kept for observation for at least a few hours.

Senate Majority Whip Richard Durbin, D-Ill., said on the chamber floor today that he had spoken with Reid and would be filling in for him in the interim.

Reid, 74, appears relatively healthy and fit, and he exercises frequently. But he also kept a more aggressive schedule than usual in the final days before the holiday Senate break. He was at the Capitol until around midnight Thursday, holding two late-night votes, and one aide believes exhaustion could be at play.

ABC News spoke with Reid on the Hill Thursday, and the majority leader appeared fine.

UPDATE 6:35 pm:

The senator's office says he has been released from George Washington University Hospital. Doctors diagnosed him with exhaustion and "not anything more serious," according to a written statement.