Queen frontman Freddie Mercury wrote this song in which he describes a descent into madness. It has a lighthearted feel, as if turning daffy might not be such a bad thing.
When he recorded it, Mercury had his wits about him, but he was nearing the end of his life, suffering from AIDS. He was in ill-health when he worked on the Innuendo album, but determined to keep making music. The album was released in February 1991; Mercury died that November and didn't announce his sickness until the day before. News of his death put the song in a different context, as the madness he sang about was likely related to his impending death.
Freddie Mercury wrote this in London with some help from his friend, the actor Peter Straker, who suggested some of the lyrics. The pair traded lines back and forth, developing the various idioms for insanity ("You're missing that one final screw," "One wave short of a shipwreck," etc.).
The song was released as a single in the UK and a video was made to promote it. Shot in black and white and directed by the Austrian team of Rudi Dolezal and Hannes Rossacher, Mercury appears as kind of a deranged Charlie Chaplin, with his Queen bandmates showing up in other absurd guises. It was one of his last on-camera performances.