Standard imaging is not effective in diagnosing the subtle neck injuries common to concussions. Your stiff neck proves that. I suggest you hang up your climbing shoes and harness for a while and work on getting your neck healed. I find it odd that the atlas chiro can predict 12 treatments. Your neck will need proper alignment and disciplined posture for a few months at the minimum to start to stabilize.

One of my challenges came when I had to start wearing progressive lenses in my glasses. I spent too much time with my head tilted back so I could see through the bottom of the lens. When I lowered the position of my display, my neck started healing.