To my surprise, it has been my experience that this turns out to be pulmonary. It was always the chicken-and-egg of... breathing.

Seems like this has been my story:

Severe prolonged stress floored me. Turns out that the autonomous control of bronchoconstriction and dilation had gone out of wack, into dysregulation. My lungs were basically clamped shut. (Muscular tension and sundry dysregulation from severe prolonged stress makes sense, right? Applies to the lungs too!)

Exercise worked when I could get myself to do it... because exercise forces lungs to open.

And the nervous system and brain, well it requires lots of oxygen. In order to learn. And unlearn.

That's interesting. I've noticed when I go for a long-enough run and my body warms up to an optimal state, breathing feels easy and effective. I wish I could breathe like that all the time.