Yup, that's the issue. This means your framerate is probably fairly low, because the vertical axis scales with that.
Bleh. Well it appears your right, but it makes no sense. In the keep, looking up and down isn't that bad. Pretty close to my horizontal look anyway. Outdoors it was a lot more sluggish. Guesstimating, my framerate outside during the intro battle was around 20-25. Looks closer to 40ish in the dungeon. Why in the world would frame rate affect the vertical look, but not horizontal look? Or even more basic, why in the hades does frame rate affect mouse look at all?? This is the first time I've ever encountered this in a game, and I have some pretty graphically intense games.
If you turn off Vsync and drop your options down low, then go look at a wall (to bring up framerate), your vertical look will be 20x as sensitive as horizontal. Too slow or too fast...either way it's annoying as hell.
How would I turn off Vsync? Through my CCC? And do I want to turn it off? Or I should ask, will turning it off benefit me only in this one regard but affect my quality elsewhere?
Getting your FPS up around 60 or more indoors also causes objects to be randomly flung through the air and then they bang around makes noises infinitely. Also VERY annoying.
See that makes no sense to me either, and I've seen others reporting it too. One person actually recommended against shooting for a high FPS in Skyrim precisely for that reason. Why would a high frame rate trigger anomalous physics interactions more than a lower one? For that matter, why does the frame rate have anything to do with the physics engine in the first place? I don't even see a remotely logical connection here. What in the heck did they do?