I’m laughing because I just managed to flip my screen while writing the title of this post.
The keyboard shortcut for rotating your Windows 10 display is Ctrl +Alt + one of the arrow keys.
Sometimes I manage to trigger this by accident. I’m not holding down Ctrl + Alt, but if I press an arrow key to go back and edit a typo, I’m suddenly looking at things on my screen sideways or upside down:
The trick to get it back?
Hold Ctrl + Alt and press your Up arrow.
Then all is right in the world, even down under in Australia.