Well done John,
2 years and many more to come. The radiated area can be v close (or include) the top of the spine and effect the nerves there. When you move your head down it "shocks" the nerves so you feel an uncomfortable feeling down to your legs.It really worried me til my rt consultant explained it. It went away after a few months after my RT. It's called l'hermittes sign/syndrome.
I get the odd painful spasm in the neck as I yawn or physically exert that area.
Your symptoms seem far worse. It certainly should ease over time.
I hated fentanyl patches. Made me feel nauseous and dozy.And as for the constipation!! I preferred to feel the pain!
You've done well -no surgery side effects. Lots of life to look forward to.
Good luck Tony K