Atlantoaxial instability usually does not cause dizziness or problems with the brain. Compression of the cord at this less usually affects the breathing and cardiac functions. Cord transection at this level is not conducive with life. So, spine surgeons take atlantoaxial instability very seriously.
If you have clinically significant instability, you should not be having adjustments done, but should see a spine surgeon or neurosurgeon, for possible surgical stabilization.
You wrote on your first posting that the chiropractor stated that "on the open mount x-ray my atlas and axis was completely "off"." That was what I was going on.
The one view of the MRI, which is for the brain, rather than for the spine specifically, the lateral masses line up perfectly with the axis. There is no widening or slipping. The lateral masses are a little unequal in size, but this can be due to slight rotation of the head during the scan.
So, from one view of a brain MRI, what is shown of the C1-C2 articulation, it is normal. But, you really can't make a complete reading off of one view. You would need to have the complete set of images read.
Unfortunately, chiropractors make a lot of money doing atlantoaxial adjustments. And, a lot a people get relief from them. However, if the mention AAI to a spine surgeon, it is a big deal to them. If an adult patient truly has rotatory subluxation of the atlas on the axis, it needs to be worked-up and treated.
While rotatory subluxation in a child is not uncommon after a sore throat, AAI in an adult is usually either congenital, due to trauma, or due to some underlying disorder (Down's being just one).
Again, if you get relief from the chiropractic manipulation, go for it. But, it would be nice to have a spine surgeon read the c-spine series, especially the open mouth view (which actually looks at the C1-C2 articulation), and not just the chiropractor.
That is an area that I would not have anyone mess around with. But, again, chiropractors do it all the time. It is really up to you, how far you want to go with the evaluation.
However, you may have to look for some other reason for the continued dizziness. It is probably not coming from the neck. There are so many causes of dizziness, from inner ear problems, neurological problems, cardiac conditions, pulmonary conditions, infections, inflammatory processes, metabolic disorders, and the list goes on.
It may be more productive to look further for a cause of the dizziness, besides the neck. Unfortunately, dizziness is so nonspecific, that it can sometimes take a long time till its actual etiology is discovered. But, you have to be persistent and keep looking.
Wishing you the best. Hope you find the cause of your dizziness soon. Hang in there.