my bearded dragon wont turn his head from side to side

Question
I have an adult bearded dragon and he is constantly holding his head at an angle like he has a stiff neck or something. He seems ok otherwise but I do know from experience with snakes that they hide illness well. He seems to use his "good side" to move himself around the tank sometime only to end up on his back.

Answer
 This sounds neurological, like "star-gazing".  But it could be something missing from his diet.  I suggest having a good reptile vet do a blood panel on him, to see if he is having a dietary deficiancy.  Once his diet has been corrected it should resolve itself.  
  To give you a good idea of a good diet for an adult dragon, it's a daily salad of collard green, dandelion, mustard greens and turnip tops, grated or shredded winter squashes and sweet potato, and then insects that have been properly gutloaded.  Then he would need a good UVB source in order to metabolize this nutrition properly, a bright white light which can be any incandescent bulb that will emit enough heat for proper digestion, and a good UVB source, a reptisun 10.0 linear fluorescent (no coil or compact types as they cause eye injuries in reptiles)or a mercury vapor bulb which will emit both heat and UVB.