Mr. Reid, who just turned 74, was going to remain in the hospital as a precaution. As a result, he will not be presiding over the Senate’s final day of business this year.

The Senate, which has been going through a tumultuous last two weeks as Republicans and Democrats feuded over nominations and legislation, resolved the stalemate late Thursday night and agreed to finish up on Friday. Senators will return in early January.

Mr. Reid’s spokesman, Adam Jentleson, said the senator’s condition had improved.