I don't think any nerve pain has to be constant. In my case, neither the cervical pain nor the TOS pain was always constant. I had/have a lot of pain that was initially thought to be mostly myofacial. In hindsight, nerve pain was at the root of it all.

I think TOS is greatly under-diagnosed. When a doctor can't find an answer, they just label you with fibromyalgia or some generic chronic/myofacial pain syndrome.