Hi there,
I saw Doctors for this same exact thing. Never did figure it out. I was just suffering with this a few weeks ago and it lasted a few weeks. I started with this 3 years ago. Was told a few years ago it might be allergies and I take Zyrtec and a nasal spray. I already new I had allergies, but I never experienced this symtom before.
Always seems to happen in August-September. When I stop to think about it, it does seem to happen when I'm stressed. Could we be tightening the muscles in the chest, diaphram area? or some sort of hyperventilating? It sure is an awful feeling. I know exactly what you are talking about. I had chest x-rays too. I think some people call it air hunger. I always seem to be fine in the morning, but after being up for awhile it would start all over again. If you find anything out, I'd appreciate hearing from you. I know we're not the only ones out there experiencing this, but even knowing that sure doesn't help when it's happening.
Take care,
Scarlett