Two German researchers, Scheibenbogen and Wirth, have suggested why this might be happening.
This is my summary as to why. Regarding home-made ORS, I'm afraid I can't advise as have no experience. Hopefully someone else can help with that.
Extract from my book:
"However, a range of recent papers by two German researchers, Prof. Carmen Scheibenbogen and Dr. Klaus Wirth, offer another compelling hypothesis for the downregulation of the RAA axis in ME/CFS. In a series of three papers, Wirth & Scheibenbogen posit a convincing ‘big picture’ thesis for the whole pathophysiology of ME/CFS, from the brain, to the endocrine, cardiac and vascular systems, right down to sodium-potassium pump cellular exchange. Their work could represent the most dramatic breakthrough in ME/CFS research to date and is essential reading for anyone interested in understanding the complexities of the illness.
[1],
[2],
[3] I will not focus on all of their ideas here but will limit my discussion to their views on the RAA axis suppression within the illness.
In essence, Wirth & Scheibenbogen believe that central to the illness’ pathophysiology is both a chronic vasoconstrictive state and a chronic impairment among vasodilatory functions. This situation is caused by autonomic changes (in the form of excessive sympathetic tone) and Beta2-adrenergic autoantibodies, both of which lead to the diminished functionality of Beta2-adrenergic receptors, which are particularly responsible for vasodilation. The result of this is poor blood perfusion and systemic hypoxia in the organs and musculoskeletal systems. As normal vasodilatory function is impaired, the body tries to rectify this state of affairs by enlisting emergency ‘back up’ vasodilatory systems, primarily through the activation of the KKS (Kallikrein-Kinin-System) and the release of bradykinin, a powerful vasodilator. While the activation of the KKS represents the body’s attempt to rectify the chronic hypoperfusion, it comes with its own serious side-effects. In particular: i) the vasodilators are powerful enough to cause vascular microleaks leading to the transfer of extracellular fluid into the interstitial space and ii) as the KKS system naturally opposes the actions of the RAA axis, it downregulates the latter thereby increasing salt and water excretion. Under this hypothesis, we therefore have two possible reasons for the emergence of a hypovolemic state in ME/CFS: the actual leaking of blood from extracellular fluid into the interstitial space and an explanation for the significant blunting of the normal RAA axis response to preserve adequate salt & water balance. From the second of these, therefore, we have a compelling potential explanation for the RAA axis downregulation that has so perplexed ME/CFS researchers. It is particularly important to note that, for Scheibenbogen and Wirth, this RAA axis downregulation will become even more pronounced during episodes of post-exertional malaise during which all of the central mechanisms within the illness will necessarily flare up. This episodic deterioration can also explain why ME/CFS patients often note that their thirst is at its worst during periods of post-exertional malaise, as during those times solute loss will increase."
[1] Scheibenbogen and Wirth, ‘A Unifying Hypothesis of the Pathophysiology of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): Recognitions from the finding of autoantibodies against ß2-adrenergic receptors’, 2020.
[2] Scheibenbogen and Wirth, ‘Pathophysiology of skeletal muscle disturbances in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)’, 2021.
[3] Scheibenbogen, Wirth and Paul, ‘An attempt to explain the neurological symptoms of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome’, 2021.