Senate Majority Leader Harry Reid was hospitalized early Friday after feeling unwell and undergoing tests that revealed nothing wrong, his spokesman said.
"Everything is normal," Adam Jentleson, Reid's press secretary, said in a statement. "He is alert, resting and feeling better,"
In Reid's absence, Sen. Dick Durbin, D-Ill., opened the chamber's last session of the year by saying he spoke with Reid and the Nevada Democrat is feeling good.
Reid could be released from George Washington University Hospital on Friday, according to a Senate official who was not authorized to discuss the topic and insisted on anonymity.
The 74-year-old Reid suffered a mild stroke in 2005.
The Senate is winding through its final day in session with a deal to confirm three of President Barack Obama's nominees, leaving dozens more for consideration next year. They include Janet Yellen, Obama's choice to chair the Federal Reserve.
The Senate approved a defense policy bill late on Thursday night and had been scheduled to hold votes on nominees overnight and into the weekend.
But under a deal between Republicans and Democrats, votes to confirm Alejandro Mayorkas as the no. 2 at the Department of Homeland Security, John Andrew Koskinen, to head the Internal Revenue Service, and Brian J. Davis as U.S. District judge for Florida were scheduled for Friday and Yellen's confirmation vote delayed until Jan. 6.