It is probably a bit of both. I don't think it's all brain. Being stuck in a state of stress from epigenetics or another other reasons is a factor. That's why my entire family has AF, even those that didn't have very stressful lives.
Here is a study where they exposed future chicken parents to stress. Many stress related genes became activated in the parents (epigenetics).
The offspring of these stressed parents had the same genes activated (expressed). The baby chicks were more agressive and competitive than normal.
That is my family ... we were all born wired. The good news is you can deactive stress related genes with meditation and other environmental changes
But.... don't forget that Hans Selye was able to make ANY rat go through the stages of GAS by exposing them to any stressor. Exercise, toxins, cold, heat ... didn't matter ... same result. You don't HAVE to come into the world with a wired nervous system to go through the steps of the general adaptation syndrome.. But it will probably speed it along if you do, since you don't return to homeostasis after stress has passed.
Eventually, the adrenals can't keep up with the stress signals, even through the stress signals are still happening. I used to feel like my gas pedal was stuck down (nervous system) ... but I just didn't have a very large gas tank anymore.
And there are people hear that respond to HC. They take an adrenal hormone and they feel better.
Women with adrenal fatigue often have irregular menstrual cycles, or they have their cycle completely stop.
Many people use pregnenolone for support and feel better. Progesterone cream was a saviour for me for about 5 years. In 2007, I had a period where my anxiety was so bad, I literally could not breath. Progesterone cream completely stopped my anxiety after about 2 weeks.
There are signs that a lack of adrenal hormones are a factor.
In regards to copper exposure, I think it is more stress and adrenal fatigue lead to reduced clearance, rather than the exposure. Sure if the exposure is large enough, even a healthy person will be overehelmed and their liver won't be able to keep up.
It's funny, because my practitioner for NB leans towards exposure being the usual cause. But my reserarch gives lots of hints that it is more stress and energy availability that leads to accumulation of copper and other toxins.
Stress leads to estrogen dominancce. Estrogen dominance leads to copper accumulation. That is probably why the progesterone cream helped me. It took about two weeks, but it probably lowered my copper levels in circulation.
Copper is removed through bile. Here is a neat article showing fish exposed to stress release less bile and are more likely develope gallbladder problems