Hi ruben, first thing I'll say is that CFS and fibro are syndromes, not diseases. We can't assume that everyone who falls into either or both of these buckets has the same underlying problem(s). We therefore shouldn't be surprised if a particular intervention allows some people to clamber out of the bucket and not others. Currently the medical profession has no ability to distinguish between these groups (if it did it would at least slap different labels on them), and it's not anyone's job in the health system to try to figure out what your particular body needs and what degree of recovery is possible. We have to do that ourselves.
Secondly, the sympathetic nervous system is an autonomic response to a threat to the body's safety. It can be triggered by either psychological (e.g. oncoming truck on the wrong side of the road) or physical (e.g. injury, toxic fumes) phenomena. I know Gupta emphasises the fact that some of these responses are learned.
I'm in the fibro bucket and have found what seems to be effective treatment, at least I'm getting positive changes and improvements in function, and while I'd never heard of the LP before opening this thread, the LP model of CFS fits my condition quite well, and I can see the role each component plays. The osteopathy connection isn't easy to explain, firstly it's more advanced osteopathy than the basic rub and crack stuff, cranial osteopathy works best for me. I have major membranes (esp dura mater) locked into a pattern of strain, consistent with pre-natal injury and stress. I've tried every professional health modality and only advanced osteopathy has been able to recognise and treat this. If you have this going on, then you may need osteopathic intervention to get better. If you don't have it going on, and I'm sure it's possible to land in the CFS bucket without it, osteopathy may not make a scrap of difference.
Even though my condition fits the LP model, there's no way in the world I could be turned around in three days once my condition had had 35 years to become both chronic and complicated by injuries and infections. I've been under treatment for over seven years, not just by osteopathy but by other modalities that have cleared away additional physiological burdens such as allergies and parasites, and only now I am starting to experience substantive and apparently permanent improvements in autonomic regulation and capacity. Had I been treated as an infant, though, my condition would never have developed. Given your long history I would give you little chance of being cured in a weekend workshop.
The role of the psychological elements is pretty simple, but to understand it you have to separate "psychological anxiety" from "physiological anxiety", something the medical establishment doesn't do (note that the medical profession doesn't acknowledge the sympathetic nervous system either, but it is a fundamental principle of biology). I am not psychologically anxious but my body maintains a chronic state of physiological anxiety. If I become psychologically anxious my body will become more anxious (which is perfectly functional sympathetic nervous system activation), the problem is that instead of increasing my body's short term capacity for action, it only devastates it. Overcoming the sympathetic dysregulation requires, among other things, getting one's body as parasympathetic as possible as often and for as long as possible. Most sufferers are caught in a cycle of positive feedback between physiological and psychological anxiety that needs to be decoupled if they are to recover. Mindfulness, awareness, etc, are techniques for recognising, isolating, and hopefully shutting down sources of both kinds of anxiety that are gratuitously triggering the sympathetic nervous response. All the available treatments for this kind of problem can only hold if the patient has some competence in this, otherwise they just come undone again. I've read the book from the Gupta package and it's all stuff I had to adopt 15-20 years before I became disabled, just so I could function. If you are skilled and experienced at managing your body you may not encounter anything new in Gupta or anything on the psychological side, but if you've never had your system checked by a good cranial osteopath I'd recommend trying that and asking them what they find.
Lastly, I think some people get turned around in a three-day workshop because while they have the physiological anxiety problem, it is being caused purely by chronic psychological anxiety, and they have no underlying physical problem. The moment they learn to stop their minds holding their bodies in a chronically sympathetic state, there's nothing stopping them from recovering. This, by the way, is pretty much the medical model of our problem.