Was in the middle of updating the index page of my WordPress blog when it suddenly decided the theme editor didn't exist and redirected me towards my 404 page. I was only content, not code.
I can confirm I can save any other page successfully.
I can also confirm, that before editor the page I saved a backup of the code before change. I've manually restored the index page to what it was previously and theme editor still apparently doesn't exist.
What the hell's going on? What could it possibly be?