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The song is about a man who is having trouble sleeping due to thinking of his lover. On the original hit single version, the track begins with Lewis singing "I couldn't sleep at all last night", and it appears this way on most oldies compilations. However, on some releases the song has a prelude, where Lewis sings "Baby...Baby...you did something to me", followed by a musical cue into the first verse. Lewis usually included this prelude when he performed the song live. According to several sources, the personnel on the original hit recording included guitarist Wild Jimmy Spruill.
Writing for Stereogum, Tom Breihan complimented the saxophone solo and called the song the "greatest insomnia-themed party anthem" in history. In 2008, Billboard magazine ranked the song as the 27th biggest song of all time that charted on the Billboard Hot 100, commemorating the 50th anniversary of the chart. It is one of only six songs from the 1960s to spend at least seven weeks in the number one position on the Billboard Hot 100.
