Chronic Fatigue Syndrome (CFS or ME) has always been a label that must have underlying causes. I have believed for years that one cause is low T3-effect within the cells. I myself was diagnosed with CFS, but I got well using T3-Only therapy. I wrote about this in my first book, 'Recovering with T3', and early on in the life of this blog.
This interesting article is entitled 'Pure T3 Thyroid and Stories of Recovery from Chronic Fatigue Syndrome (ME/CFS) and Fibromyalgia: An Overview.', I think you'll find it interesting: