So I actually went to tons of doctors, my GP, neurologist, cardiologist (also had chest spasms). I got an MRI of my head, but not my neck, as the docs thought it was a head issue with all the headaches. I got an x-ray eventually as well but they didn't see anything they thought would matter. I did have a little misalignment in the x-ray but the doctors thought it was nothing.

My neck also felt unstable. Like my head would "slide off" if I tilted it wrong. My cervical vertebrae also would click in certain positions.

It was actually a physical therapist that fixed it. I had gone to them to "stabilize" my neck. They noticed that I couldn't turn my head to the left as far as I could to my right. We did ~2 months of exercises and one day they tried manipulating one of my cervical vertebrae and it was like night and day. I felt a rush of blood up into the left side of my brain and that night I slept great. It took a couple more weeks of exercises to stabilize the new position (other things started to move now that it was better aligned). And I haven't had any issues since.

I hope it's the same for you! I understand what it's like and it's awful. I think in my case it was more of a rotation problem so that might not show up as well on x-ray. Idk what other imaging would be better (if any). It might be worth getting a physical therapist to check out your neck mobility and see if there's anything noticeable. Best of luck.