You are in softproof mode.
So, whenever you make any develop edit changes Lightroom will ask you if you want to save it as a proof.
The keystroke 'S' in the Develop module toggles the image in or out of the softproof mode, so in the situation as described above pressing 'S' should exit the image out of softproof mode.
OH THANK YOU!!! It was driving me crazy. I can't blame the cat, tho!!
Your cat has put you into Soft-proofing mode. To get out of that, press "S", or uncheck the Soft-proofing option in the Toolbar (press "T" to show the toolbar).
SO funny. Literally the exact same thing happened to me! My cat walked on my keyboard and it was driving me nuts!
Haha, my cat just did that too, which is how I ended up on this page!
I've decided to never learn how to turn off soft proofing so I can google it and come to this page a few times a year. Thanks guys.