This happened while I was on this Forum yesterday and I considered posting here to see if I could get a solution, so felt I had to share what happened. I was holding a clipboard with some papers on top of it while reading, and evidently the board hit some key on the keyboard and suddenly everything was sideways!!! I couldn't find any way of changing it. And, it also affected the mouse, which was very weird and hard to control. I managed to do some things I had to do sideways, but manipulating the mouse made it almost impossible.
When I called my computer technician, his assistant got on the phone, told me to press Ctrl + Alt + Up Arrow - and everything was fixed, the display and the mouse!!!! I still don't get the connection with the mouse and he didn't really explain why it would be connected to this, but all was well - PHEW!!!