Nicky, I'm sorry but the first mistake is that fact that your NEURO checks your breathing!!! His mistake, not yours. You need a pulmonologist. I cannot stress that enough. They are the experts in that area, not the neuro. AND he should not "act" like a pulmonologist. Very dangerous - for him and you.
Is he a board certified pulmonologist?!!! Would "you" ask an endocrinologist to be an OB/GYN? An infectious disease doctor to be a rheumatologist?

I'm not angry at you but at your doctor for not referring you for better, more specific testing. And an arterial blood gas, if that's necessary.
Yes, you absolutely need a nose plug when doing those tests.
I'm sorry you aren't doing well. I hope the plasma will help.

Annie