Dear Stephanie:
Yes, anxiety is physical. Everything we experience, our thoughts, our feelings, everything is physical, possible only because we have a brain and the rest of the body.
What people refer to as “psychological”, or “mental,” as in not physical, is physical, only those things cannot be measured in a physical test like a blood test or an X Ray. Maybe in the future science will make it possible to detect and measure such physical events as that occur when we think and feel anything at all.
I experience anxiety still, a lifetime of anxiety. Was on psychiatric drugs for 17 years, including Klonipin and got off them all a few years ago. Regarding my breathing I hold my breath, breathing shallowly, but not struggling to breathe, like you described, as I understand it. This very morning, a moment ago, I felt the discomfort of it, that panic surge. I am very familiar with it. There is a way to stop the panicking element in anxiety, that is the fear of the fear itself. The fear of the fear taking over. The escalation of fear can be stopped through practice.
I hope you post again and I will be glad to reply again, if you’d like.
anita