Using PC version through Steam, GOY Edition, no mods.
I have noticed more than a few people have had this complaint. When performing a finishing move sometimes your camera angle will switch to third person so you can see the kill happen as sort of a cut scene. For various reasons this camera angle can get stuck permanently so you can move your character around but the camera angle doesnt move with you causing you to walk off the edge of the screen (for me it was a drauger hit me with FusRoDah while I was getting a kill).
Normally you just load an old save & continue on; but I, like many, forgot to save for a while so I would have lost a lot of work. I messed around with it for a bit & I think I figured out how to shake the camera loose but it's not easy. You have to trigger the kill cam again. I COCed to Whiterun & shot a guard with my bow. the kill came followed the arrow & he died. When it was over my camera was back to normal & I had a bounty of 1000 in whiterun. :P
I don't know if this has already been posted elsewhere, but if it is I couldn't find it so I'll post it here. I hope this helps some other people who've had this issue.