My PT did what I would term cervicogenic PT. She had me on my back and would make sure my jaw was not in spam, my shoulders where not in spasm and with apply a bit of traction to my head and gently manipulate C-1 and C-2 and rock my head while doing it.

Then, it was up to me to be disciplined with posture as the ligaments strengthened. It was a few months before lasting improvements were noticed. A few years before I could stop being disciplined with my sleep posture.