Hmmm.... sounds strange. Does it only happen in the FM2, and if yes, with consistency?
Check your stick map, maybe the hat got "remapped" somehow? Or the head position is adjusted in a way that makes it look right back? Does it happen if you look right with your numpad (not hatswitch)?
Another posibillity would be your hatswitch being dirty/going out on you.
Other then that, i dont have any bright ideas about it....
Edit: Heres two screenies.
The first one is the look right with head position all the way back. The second one is actually look right back with default head position.
Maybe you just have a funny head position saved.