Is it possible that you accidentally typed *a# into a GMail window? Those are the keyboard shortcuts for "select all" and "move to trash".
Fear of doing that sort of thing has led me to disable GMail keyboard shortcuts altogether on my account. (To do that, press ? in a GMail window and click the link on the second line of the overlay window.)
I searched what I /thought/ was EVERYWHERE yesterday. Thank you thank you thank you!