Similar happened to me a few years ago.
We used to play in two different tunings (we had an accordion player who jammed on certain songs who had to be in standard)
Rather than tune up and down we used two different guitars.
We started our set with Crazy Little Thing Called Love. After two or three bars, I realised I had the wrong guitar on.
As I am also the singer I had to try to play one fret out, which was a nightmare as I was trying to sing too, plus some of the song involved open strings.
I managed one verse and chorus and then we had to stop and apologise.
I wanted the floor to open up.