Sen. Robert Byrd, D-W.V., was taken to a Virginia hospital Monday after his caregiver noticed he was running a fever and feeling lethargic and sluggish, NBC News reported, citing Byrd's staff.
The caregiver called Byrd's doctor, who recommended Byrd, 90, go to the hospital for overnight observation, according to communication director Jesse Jacobs. Byrd was taken there by ambulance.
The senator had been working on Capitol Hill earlier in the day, and had blasted Vice President Dick Cheney for insulting his state.
Talking about his family roots and how he's distantly related to Democratic presidential candidate Barack Obama, the vice president noted that he had Cheneys on both sides of his family.
"And we don't even live in West Virginia," Cheney quipped.
Byrd responded by saying that for a vice president to openly display "such contempt and astounding ignorance toward his own countrymen" was an insult to all Americans.
In late February, Byrd was hospitalized after a fall in his home. About a week later, he was treated for a urinary tract infection.