A lot of people ask me that. How lucky they are to not be acquainted with the world of nebulous diseases. Chronic fatigue syndrome is what I choose to call my condition for convenience. I have been diagnosed with it officially, but I have to stretch the symptom checklist a bit to fit me. Like our myriad psychological diseases, chronic fatigue is simply diagnosed by how many symptoms you have on a checklist. If you have one too few, you don't have it.
CFS doesn't have a definitive test or biomarker like diabetes or cancer at this point and therefore isn't a “real” disease in the eyes of many. It falls into a category with fibromyalgia, multiple chemical sensitivity, and chronic Lyme, diseases that are most likely, on a standard doctor's visit, to garner you a blood test for anemia and vitamin D deficiency, and flippant prescription for anti-depressants/anti-anxiety medication without even so much as a recommendation to see a therapist.