I thought I should probably tell you a little more about myself, particularly my illness - I might be repeating myself in parts, but try to bear with it. CFS may well be a group of similar illnesses, or a single illnesses with different causes, however you want to put it. LDN might not help all of them. If your case is similar to mine it's probably likely that LDN would help you. Some cases of CFS seem more like chronic hypersomnia and somnolence and since LDN isn't a stimulant it probably won't help those people.
Apparently some cases of CFS are caused by bacteria, eg. Chlamydia pneumoniae, Coxiella burnetii, Borrelia burgdorferi (that's Lyme for you) and the different mycoplasma species. In some cases the bacteria is still lingering in the body and with proper antibiotic treatment (sometimes with other adjuvant medications) you can cure the CFS or at least make it a lot better. In other cases the bacteria may cause an immunologic reaction (similar to rheumatic fever and thus antibiotics are not of use, except for their anti-inflammatory properties. Someone I know was diagnosed as having CFS due to a past food poisoning due to campylobacter.
I don't think bacteria had anything to do with my own illness. In February 2000 I got a strange infection with no congestion or respiratory symptoms and a fever that went up and down for a week. I didn't have any appetite, I was incredibly weak and my muscles and lymph nodes hurt. It could have been influenza, but I've had the flu once and it felt quite different. Later I postulated it could have been Epstein-Barr virus (the one behind mononucleosis) acting in atypical way, but when I was tested in 2005 turns out I have no antibodies to EBV. It could have been cytomegalovirus (another herpesvirus which is connected to persistent fever) though, as I have antibodies to it.
The infection recurred in April 2000 and left me with a poor appetite and other sequelae for weeks. But I thought I did get better. On the 28th of August 2000 I got a fever and it never went away. Soon I started to get heart arrythmias, panic attacks and some other symptoms. I was fatigued too, but I blamed it on other things. Other symptoms (cognitive dysfunction, orthostatic hypotension, aches, migraines, hair loss, muscle weakness, urinary frequency, nausea, rashes, IBS, huge suspectibility to bacterial infections etc) appeared with time.
I am personally convinced that my illness is postviral, either caused by a "hit-and-run" bug sparking an immunological reaction, or due to a virus still wrecking havoc in my body. The infection doctors at the Helsinki university hospital never managed to find evidence of any infection running rampant in my body, though it's possible that I have an active CMV infection. However they don't treat CMV, only EBV (with Valtrex), so I was out of luck on that front. And since I didn't have IgG deficiencies, I didn't get intravenous immunoglobulin either. I believe it would have helped me.
I am pretty much a textbook case of CFS, except for a few things. CFS usually isn't progressive, but in my case it has been. I don't really have chronic pain and I've only had significant muscle weakness for less than two years. In the early years of my illness I was able to exercise a lot, it was cognitive activity that totally wore me out. Maybe I exercised too much and thus caused damage, but the illness was progressing even before that.
It's also a bit unusual to be helped so much by corticosteroids, but I know some other cases as well. I've never had a serious reaction to a medication or supplement, in general I never have problems with them. But unfortunately I've never been one of those CFSers who never catches any bugs, but one of those who catches every one of them and gets very ill. I've had so many bacterial infections in different parts of my body that I've lost count. I once spent 12 days in high fever due to parainfluenca. But now my supplement regime - and perhaps other things - have helped with this and nowadays I don't get colds very often. And if I do, it's often fairly mild, which was previously unheard of.
My bloodwork is pretty normal for a CFS patient. No gross abnormalities, but my ESR is very low, which is common in CFS (even though some people have a high ESR). My cell counts are usually normal, but besides that my immune system is similar to that of an AIDS patient, consistent with a Th1->Th2 shift: eg. low IgG3, high IgG4, somewhat high IgE. I've never had ANA, ANCA or any other autoantibodies detected in my bloodwork, but if you have those, it's probably likely that LDN would work for you since it works so well for autoimmune conditions. I believe that having clearly immune, autoimmune or allergic symptoms as a part of CFS is a good indicator that LDN would likely work for you, but that's merely my speculation based on the scientfic evidence.