When you realize you've read more Elder Scrolls lore in the last 10-years than you have "real" history, religion or science.
When you find yourself unconsciously subbing TES-friendly lyrics into songs: Aedra in place of angel, daedra in place of devil, Nirn in place of Earth, Oblivion or Void in place of hell, etc. Recently my officemate was listening to Over the Rhine, and I caught myself singing "I want to see you smiling, on Sundas afternoon", in a song that I mentally renamed "Nirnbound Lovesong".
I clearly have problems.