I have been trying to figure out this exact same thing. I can’t answer your question other than to say that I’ve had one surgery so far and now that side does not experience these episodes quite as much (though I’m still a few weeks into the healing process). For what it’s worth, Dr. Nakaji dismissed CCI in my case very quickly (I never had any symptoms or signs of CCI prior to my IJV compression). I’m guessing that as pressure builds, nerve and muscles structures are also pressed down giving us that stiffness. I still get it after surgery on that side but less often, and I can usually sit in a hot shower and stretch it out to make it feel a little bit better.
I also can’t offer any insight to your situation, @Luckee7, however, we’ve had a number of member recommend myofascial release therapy post op as that has been very helpful for them. I think it can take a number of sessions to be very helpful, but it’s a gentle approach that could help reduce the stiffness in your neck which might in turn help reduce the other symptoms you’re experiencing.
Would heat as @RobotEagle suggests help, or would that give you more head pressure? I have neck stiffness but it’s definitely muscular, would very gentle PT help as well as trying myofascial release massage, I’ve find that helps me too.