It can contribute. So can low blood volume.
This article and
this article on Health Rising explains more about it.
Some people with CFS/ME have had blood transfusions, or saline IVs and have felt 'almost normal' for a short time after. Both of those procedures can raise blood volume.
Others have found that raising BP by using desmopressin or other meds; compression garments; even G-suits, have been helpful for reducing symptoms.