Birdlady, did your blood tests show low levels of natural killer cells? That seems to be a marker for CFS. Once more serious diseases that cause low NK are ruled out, then a diagnosis of CFS can be made. I believe that CFS is caused by mercury, other toxic metals, or other toxins. I guess testing the blood for NK cells is a way someone can prove they are sick if they need to apply for disability benefits, or to convince family members that they are sick.