I know what you are talking about. The physical response to fear or even the memory of fear can be intense and measurable.
I used to have severe high blood pressure (off the charts) as a side effect of dealing with my PTSD my blood pressure readings are now normal or even low normal. Heart rate, breathing, blood pressure, digestion, vision, hearing, all can be altered by a stress response. I spent years learning and teaching martial arts and meditation, turns out I was just getting better at repressing my symptoms and they would just keep getting stronger.
If you are dealing with your problem in the right way, the physical response will go away. You can't change the fact that the human body responds to stress in a physical way, but you can reduce the stress impact. Do some research on Mindfullness meditation, look for Jon Kabat zinn. It is used in many aspects of medicine, especially pain management.