Hi Synapse, I'm finally getting back to this thread...
You said your life has been similar to mine. Does that mean you also experience little or no abnormal anxiety? I assumed you did since you titled your thread, "Why do people get shy and stressed?" Anyways, if your anxiety levels have changed at all, that's further evidence that something good has happened. Of course, I can't say exactly what.
Maybe I wasn't very clear, but I don't feel frightened of ordinary social situations. This has been a source of frustration to me when I've spoken to counsellors about this: they hear about how empty and isolated my life is and assume I must feel anxious about being around people and need to "practice" being relaxed in simple, everyday interactions. It's more like I'm frustrated with not being able to get anywhere satisfying with people, so I've just given up. And that I find it hard to relate to others because their lives have been so much fuller than mine, and I wonder what I have to offer anyone since I've had so many years with nothing in them...well there's a lot to it, but it's not really about anxiety.
I have no reason to believe there is an underlying physical problem. I am not generally an anxious, harried person. Plenty of things are stressful to pretty much anyone, and I've handled them as well as most people (final exams, class presentations, busy workplaces). If I had an underlying physical problem that made me prone to enhanced stress responses, I'd have experienced plenty of that in the past few years. I did have many fears as a child; most of them eventually extinguished themselves. The social anxieties stuck around longer (they're very easy to reinforce, since feeling anxious and self-conscious make you prone to bad social experiences and interpretations that further support your fears) but even those faded eventually (with the help of certain changes in my life, and possibly some reading about cognitive therapy--it's hard to say). I never changed my diet much or anything like that.
Also, as you said, the endocrine system affects far more than the stress response. When people have medical issues that affect it, they can have substantial weight changes, changes in sleep patterns, digestive problems, hormonal fluctuations that lead to noticeable abnormalities such as masculine facial hair growth in women, major abnormalities in energy (either exhaustion or inability to sleep), skin changes, etc. Anxiety alone is unlikely to mean an endocrine system problem. (Don't know if you have other health problems, but I don't.)
The latest article you linked to ("Epigenetic programming of neuroendocrine circuits in development to ageing"), stated that the researchers looked at brain tissue; the factors in the brain that regulate the HPA axis. Activity here is regulated by the brain, and epigenetic or genetic factors can increase its reactivity, like they mentioned. That means they can strengthen the stress response, cause it to occur more often, or cause it to be slower to calm down in response to later signals (this last one seemed to be responsible for the differences in stress-prone rodents in the article I mentioned above). It still doesn't just generate high-stress states on its own. It still needs a signal from the brain. And, if neurological controls are causing increased reactivity of the HPA-axis, then it's going to follow the brain's instructions and be more reactive. That doesn't mean it's unhealthy; it means it's doing what the neurological controls are "telling" it to do.
So no, I don't see how you're getting the idea that epigenetic changes and adrenal burnout syndrome are the same thing at all. Your quote mentioned that stress can be one risk factor for adrenal problems, not that adrenal problems are the root of anxiety disorders. Also, the quoted material sounds like it comes from an alternative health site. As a general rule, I don't trust these. Most of the ones I've seen promote odd theories without convincing evidence to back them up.
Epigenetics is a fascinating area. I like how they mentioned that epigenetic changes can occur throughout life, they can be reversible. I wouldn't be surprised at all if some of these changes had happened in my own body after the stress in my life was reduced and remained lower over a period of time. Maybe there are also certain ages in which permanent changes are more likely. I know the brain continues to develop until age 24 or 25, so perhaps the opportunity for personality changes is greatest before this age? On the other hand, stress and anxiety have plenty of negative health effects, so it would make sense that the changes that cause increased reactivity would be reversible. People would benefit most if changes can happen in both directions.
Anyways...that's all for today.