Charlie1 If I remember correctly, Mestinon is used in myasthenia gravies to aid muscle power. If this had a similar effect in yourself, you'd perhaps have a stronger cardiac pump, better circulation (possibly?) better blood flow to the brain (clutching at straws here) and less symptoms,so feel 'better'. But....that doesn't explain the neurological dysfunction and symptoms though, so I'd have a guess at you're inadvertently affecting an undiagnosed autoimmune process in your central nervous system, by taking Mestinon. I say undiagnosed, as the latest research on POTS, suggests it (or subsets) is an autoimmune disease.
http://www.dysautonomiainternational.org/blog/wordpress/new-evidence-of-autoimmunity-in-pots/
http://jaha.ahajournals.org/content/3/1/e000755.full
To my knowledge, there are no commercial assays for autoimmune POTS (Other than one from the Mayo clinic, a autonomic panel), yet that doesn't cover the latest research findings. So if you wanted to do a little science study of your own, you could try and measure your levels of cholinesterase in your blood. But, I guess, these are not reflective of brain levels, which would at the least require a spinal tap (lumbar puncture) or a specialist brain scan.
This study might have some connection perhaps? I know it's 'CFS', but organic CFS (potentially ME), is often linked with POTS.
'The research group is therefore confident that the findings of increased sensitivity to acetylcholine in CFS patients are robust and unusual. Increased sensitivity to acetylcholine is normally associated with trained athletes, while CFS patients are characterized (according to the Fukuda 1994 definition) as having "a substantial reduction in previous levels of occupational, educational, social or personal activities". These results are important in terms of vascular control mechanisms in this patient group and may be relevant to the problem of orthostatic instability that is so evident in most CFS patients. The findings reported in this review are specific to endothelial cholinergic activity and may or may not be applicable to other more widespread neurotransmitter functions of acetylcholine. Recent evidence in a very small group of patients suggested that CFS might be the consequence of a cholinergic dysautonomia, and that treatment with cholinesterase inhibiting agents might well be therapeutic'.
Source:
Acetylcholine Mediated Vasodilatation in the Microcirculation of Patients with Chronic Fatigue Syndrome.
http://www.ncbi.nlm.nih.gov/pubmed/15041034
I but that in red text, as Mestinon, blocks cholinesterase.
So maybe, by taking the drug, you're inadvertently messing with this process, or the vagus nerve maybe? Lots of autonomic symptoms are caused by vagus nerve dysfunction, including in POTS and probably ME.
I hope you get your health back soon, any improvement is good news and loss of function is of course infuriating. Maybe you could try some other medications or investigate why Mestinon helped you so much, with some form of endocrine testing such as blood volume assessment (very hard to get), or more 'simple' tests such as seeing if your Renin/Aldosterone ratio is haywire. It usually is in POTS patients. Also if possible I would measure your Vasopressin (ADH), especially if you pee too much and/or if it's clear colour. If so, I'd tell your doctor and ask for a water loading test, water deprivation test to make sure your POTS diagnosis is accurate.
Have you tried Midodrine? If you aren't overweight or don't run a higher BP, although it has lots of side effects and needs to be tested in a Hospital first, Midodrine can helps some people with POTS gain significant function back, by constricting blood vessels, and thus keep more blood from pooling in your feet. If you haven't tried this drug, and your doctor says you meet the criteria, you may want to consider this medication too. In layman's terms, it's Parkinson's drug, so 'safe', but you'd need to be given it by a specialist or a cardiologist.
Good luck and take care.
