I would like to ask you which organ system is 'subjectivelly' affected the most in your illness: 1. CIRCULATORY SYSTEM: pumping and channeling blood to and from the body and lungs with heart, blood and blood vessels. 2. DIGESTIVE SYSTEM: digestion and processing food with salivary glands, esophagus, stomach, liver, gallbladder, pancreas, intestines, rectum and anus. 3. ENDOCRINE SYSTEM: communication within the body using hormones made by endocrine glands such as the hypothalamus, pituitary or pituitary gland, pineal body or pineal gland, thyroid, parathyroids and adrenals, i.e., adrenal glands. 4. INTEGUMENTARY SYSTEM: skin, hair, fat, and nails. 5. LYMPHATIC SYSTEM: structures involved in the transfer of lymph between tissues and the blood stream, the lymph and the nodes and vessels that transport it including the IMMUNE SYSTEM: defending against disease-causing agents with leukocytes, tonsils, adenoids, thymus and spleen. 6. MUSCULAR SYSTEM: movement with muscles. 7. NERVOUS SYSTEM: collecting, transferring and processing information with brain, spinal cord, peripheral nerves and nerves. 8. REPRODUCTIVE SYSTEM: the sex organs, such as ovaries, fallopian tubes, uterus, vagina, mammary glands, testes, vas deferens, seminal vesicles, prostate and penis. 9. RESPIRATORY SYSTEM: the organs used for breathing, the pharynx, larynx, trachea, bronchi, lungs and diaphragm. 10. SKELETAL SYSTEM: structural support and protection with bones, cartilage, ligaments and tendons. 11. URINARY SYSTEM: kidneys, ureters, bladder and urethra involved in fluid balance, electrolyte balance and excretion of urine. 12. ENDOCANNABINOID SYSTEM: neuromodulatory lipids and receptors involved in a variety of physiological processes including appetite, pain-sensation, mood, motor learning, synaptic plasticity, and memory. For me it is (subjectively) definitely the nervous system: Since the sudden flu or mono-like onset twelve years ago I have felt that it is mainly the brain that is affected: Impaired balance and motoric coordination, dizziness, dementia-like cognitive deficit: substantial decline in IQ score, diminished attention span, poor memory, neurological physical exhaustion, feelings of derealization, visual disturbances, constant tinnitus, constant localized headaches. Then, to a much lesser degree, it is (again subjectively) the immune system: I am catching an abnormaly high number of infections. In the past it was about fifteen viroses or 'colds' during one winter etc. Otherwise all other organ systems seem to be completely 'healthy'. Perhaps I am an exception but I don't read any articles about ME/CFS that deal with abnormalities in muscles, hearts, lungs, arthralgias, myalgias, pain thresholds etc. Is there anyone else here, who feels that the brain is the primary and most affected organ in his or her ME/CFS?