Piglet, you actually completely understand it, and your analogy is spot on from everything I know about the autonomic nervous system (we get taught everything on the PTSD course to help, hence why I recommend it to anyone with Australia).

Maybe its time I pull my finger out and start pulling out more of my notes to put up here about this exact thing, which will show everyone a bit more depth, in a simplified manner, what is going on within us in this facet? I think I will do that....