Yup, it can be done. People are always completely befuddled and amazed when this happens. It can even be turned 90 degrees. It is actually a feature in Windows. If this happens accidentally to you, you can return it to your normal view by holding down the Ctrl and Alt keys and pressing one of the arrow keys. You may have to try different ones until you can get it right-side up.
Alternatively, Right-click on the desktop, choose Graphics Options, Rotation