It is difficult to diagnose an upper neck injury specifically other than by the ways already mentioned. But, you already mention neck pain. A PT may try to check you with range of motion movements. These can be helpful before treatment starts but should not be done during following treatments for a few weeks or even months. Each range of motion assessment can inflame the area being treated. Treatment should be very gentle. It should be just enough to maintain mobilization of C-0 to C-1 and C-1 to C-2.

Mine has stabilized but never healed. I can move my head and feel/hear the grating. These joints have very little cartilage to lubricate movement.

The important issue is to be sure they are not locked and the ligaments have an opportunity to strengthen/tighten so as to hold the joints in position.

Increase vision acuity can add stress to the brain as it stitches each image together. Some optos will prescribe a detuned prescription so the eyes can relax as the brain does not need to work so hard to stitch the fuzzier images together. My optometrist detunes my normal prescription just a bit because it offers a more comfortable vision. He showed me the difference with his testing equipment until we found a comfortable level. Some PCS sufferers do well with a pair of glasses that correct to 20/40 for those 'relax my eyes' time.

You should try limiting the amount of time you spend reading and doing screen work to see if it helps with your headaches.

I would get to point where I fatigued and needed to reread a line of text. This was a sign I needed to take a break.