Kind of interesting that you mentioned the issue with C5 and C6, I also have an issue with that area. They called mine congenital fusion, meaning it was that way since birth. I don't really buy that, because I had a very nasty car accident in 1981. They only did regular x-ray at that time, really did not should the fusion, so???
I have always keep this in the back of my mind and felt that it has something to do with headaches/dizziness/swallowing issues and etc. After enough pain and complaining, I finally got a Dr to order an MRI (which showed the fusion), Because of the fusion, we still don't know what nerves might be effected, pinched or compressed. Wearing a motor cycle helmet seems to bother the most, adding weight to that area of the neck.
They say there is nothing we can do at this point, just live with it!
I should not complain I guess, can still walk, talk, eat and pretty much do everything I want, so it is what it is!