I have lots of experience with the activator. It can be very good but was not much help with C-1 for me. C-1 does not have facets like the lower vertebra. C-1 is held in place mostly by ligaments. One value of the activator is simply that it is gentle, especially when compared to the twist the head and pop the neck. The risk is low.

I bet the issue is more inflammation that interrupts blood flow that can impacts the brain stem (autonomic nervous system) and blood flow that supplies 25% of the brain. There may be some radiculopathy (nerve impingement) if you have neck muscle spasms. Radiculopathy would usually be C-1 to C-2 and lower, not C-1 to occiput (skull).