"The pain was real, and they don't know what caused it," Limbaugh said.
Asked whether he was taking painkillers, Limbaugh said no.
His medical problems have attracted attention in the past. In 2003, he acknowledged an addiction to pain killers for severe back pain and took a five-week leave from his radio show to enter rehab.
Limbaugh couldn't resist a few political comments in the short press conference at the hospital. He said he got the best health treatment in the world "right here in the United States of America."
"I don't think there's one thing wrong with the United States health system," Limbaugh said.
Caller after caller to his show Thursday sounded their well-wishes, asked to simply say "ditto" -- a traditional Limbaugh catchword -- so they could get on with questions and comments on social and government issues on the national talk show. Friday's show was a Best of Rush special.
Americans in a poll last month called Limbaugh America's most influential conservative voice, and more than 14 million people hear him at least once a week, making him the nation's highest-rated broadcaster.