when getting on your horse aim your view down as much as you can. next take your saddle from your inventory and place it in the horses saddle slot. by doing this your screen (in the background) will turn upside down. when you exit the screen and/or take the saddle off you screen will rotate to a normal position. I've noticed its a very uncommon situation and i have not been able to repeat it.
Duplicate of MC-16180, please use the search function to see if your bug has already been submitted. Currently over 58% of tickets are being closed as duplicate.