Welcome to Healingwell, Helen.
CFS patients are like Christmas chocolates - a very assorted bunch ! In many cases, the same sorts of symptoms seem to be triggered by different root causes, particularly where there is an autoimmune disorder involved. So whether or not I have CFS, CFIDS, PVFS, ME or whatever you want to call it is a good question. Since there's an ongoing debate raging on both sides of the Atlantic as to what exactly constitutes these "syndromes", or whether they even exist except in the mind (why believe the patients ? They're not medically trained, seems to be the thought), diagnosis is always a real problem.
Hope this helps you, from your post I'd guess you have no brain fog, but if you are finding it hellishly hard to concentrate on reading and writing then you are a typical ME/CFS sufferer ! (The answer there is to break it up into sentences, and just read one sentence at a time - have a complete break between each one, and ignore anything irrelevant.)