According to the title of her single, what was Peggy Lee suffering from in the 1958 pop charts?

"Fever" is a song written by Eddie Cooley and Otis Blackwell, who used the pseudonym John Davenport. It was originally recorded by American R&B singer Little Willie John in 1956 and released as a single in April of the same year. The song managed to top the Billboard R&B Best Sellers in the US and peak at number 24 on the Billboard Hot 100. It was received positively by music critics and included on several lists of the best songs during the time it was released.

In May 1958, Peggy Lee recorded a cover version of the song in Hollywood, which featured significantly rewritten lyrics composed by Lee herself without credit. "Fever" was not included on Lee's album Things Are Swingin' when it was first released in 1959; however it was listed as a bonus track on its 2004 reissue release.

Lee's cover, most likely arranged by the singer herself (despite the official credit to conductor Jack Marshall) was a more slow-tempo version than the original; it was described as being in "torchy lounge" mode, accompanied only by bass (played by Joe Mondragon) and a very limited drum set (played in part with fingers by Shelly Manne), while the finger snaps were provided by the singer herself.