I would have your cortisol levels checked. I have had CFS for 16 years and like you had returned to a reasonable level of life, then suddenly started going downhill. Pressure in head, dizziness, endless fatigue, pain in abdomen, etc, etc. It turns out I have Addison's disease. This is rare, so unlikely for you, but you could have mild adrenal insufficiency that would be helped immensely by taking a small amount of hydrocortisone daily (maybe as little as 2.5mg). Get your doctor to schedule a synacthen or ACTH test for you.