Oh holy SHIT, it's the F11 key that does that horrible thing I always end up closing the window out to correct. I've been accidentally hitting it for YEARS and knew it was some kind of keyboard command, but was unable to trace exactly what I did wrong or how to undo it. This will actually improve my quality of life from here on out. WIN!
(also I think I don't get to call myself a geek for a day or so... I really should have figured this out literally YEARS ago)