Hi, Sasha.
In my hypothesis, the low blood volume in CFS is caused by central diabetes insipidus (not to be confused with diabetes mellitus). People with CFS do not produce enough antidiuretic hormone (vasopressin). The result is that the kidneys dump too much water into the urine, and the person becomes thirsty and drinks a lot of fluids, but never catches up with the loss, and thus develops low blood volume and the problems that go along with that (such as OH and POTS).
The low secretion of vasopressin occurs because of glutathione depletion in the hypothalamus, in my view.
To raise glutathione, it is necessary to correct the partial block in the methylation cycle.
If you want to read more about this hypothesis or the treatment that is based on it, go to
www.cfsresearch.org and click on CFS/M.E. and then on my name.
I hope this is helpful.
Rich