CFS (ME/CFS) has many standard and obscure "causes". Those afflicted with CFS feel profoundly weak and exhausted...and may have some other symptoms, too. It also loosely falls under the heading of "chronic fatgue & immune dysfunction syndrome" (CFIDS) & Multiple Chemical Sensitivity (MCS) & Environmental Illness (EI), & "dysautonomia" (the old time name...19th and early 20th centuries...of which was "neurasthenia"...in bygone times, almost an exclusive ailment of females taken very seriously by physicians & laymen alike).

Variations of what "neurasthenics" suffered are today called (or loosely include): CFS, CFIDS, vasovagal syncope,neurocardiogenic syncope, panic attacks, inappropriate sinus tachycardia (IST), "mitral valve prolapse syndrome", irritable bowel syndrome (IBS), postural orthostatic tachycardia syndrome (POTS), & fibromyalgia. All of these center around some aspect of an apparent imbalance, even peculiarly volatile, in the autonomic (which has sympathetic & parasympathetic components) nervous system. That autonomic system affects "unconscious" bodily functions, which functions are closely related to "fight or flight" issues, "heart & mind" issues, and even spiritual issues or conflicts...maybe even issues of "right & wrong". While dealing with doctors, jobs, & family when initially sufferingg with these dysfunctions can make you feel crazy (or worry that "people" think you are crazy), they are not psychiatric "craziness". Many have a significant psychosomatic (functional) component. Two dramatic sometimes stress-induced acute diseases (therefore, "functional") are acute-illness or stress-induced acute telogen effluvium (ATE)(generalized scalp hair loss [alopecia]) and acute-illness or stress-induced urticaria (suddenly appearing skin whelps or "hives" which itch.

• Common causes:
  • chronic hyper-anxiety. Vestibular type balance disorders...such as the rare "mal de debarquement (MdDs), or disembarkment syndrome" (not "spinning" dizziness but a rocking, boat-in-waves sensation)...tend to be associated with anxiety & panic attacks).
  • "burnout". Take the on-line test for burnout HERE.
  • psychological depression
  • undiagnosed or poorly controlled diabetes
  • sleep disorders: to include strangling & coughing as part of gastroesophageal reflux disease (GERD).
  • anemia of any type ("low blood")...which may include low counts of other blood cells (pancytopenia, bicytopenia, leukopenia, thrombocytopenia).
  • CFS: idiopathic/unknown causes (chronic fatigue & immune dysfunction syndrome...CFIDS; dysautonomia; postural orthostatic tachycardia syndrome [POTS])...the type possibly rooted in spiritual dysfunction [details of Martha's miraculous cure] [treatment program in Georgia]. CDC definition HERE.
  • iron deficiency, systemic (not necessarily anemic)...can also cause hair loss (alopecia).
  • perimenopausal state/phase in life.
  • chronic lung disease (emphysema/COPD; asthma; etc.).
  • chronic heart disease (myopathy; subclinical or clinical heart failure [CHF]; etc.
  • chronic vascular insufficiency to the brain.
  • elderly: combined factors, to include depression, organic chronic disease with various pains & discomforts, growing apathy about life, polypharmacy (effects of being on lots of meds), and physical deconditioning (progressively getting further out of shape due to increasing physical disuse of one's body).
  • low testosterone levels (low T) in men (especially in diabetics).
• Less common causes:
  • low blood sugar (hypoglycemia).
  • hyperthyroidism (overactive gland)...especially in the ELDERLY.
  • hypothyroidism (underactive gland).
  • sarcoidosis (90% have pulmonary lesions/adenopathy and 25% have skin lesions [usually a type of face bumps...sometimes scaly plaques on extremities]; and most have elevated ACE blood levels).
  • chronic infections: viruses, bacteria (hidden abscesses), parasites (amebiasis), spirochetes (lues; Lyme disease).
  • viral syndromes, chronic:
    • EBV-type chronic fatigue syndrome.
    • HHV6-type chronic fatigue syndrome.
    • CMV-type CFS.
    • parvovirus-type CFS.
    • enterovirus-type CFS.
  • post-viral syndromes
    • "post-polio syndrome" years later in polio survivors.
  • hemochromatosis.
  • apathy (masking as fatigue): normal pressure hydrocephalus (memory loss, gait problems, mood & reasoning ability changes).
  • lupus and other autoimmune disorders.
  • brain neurotransmitter deficiency (CRH and/or other secretagogue deficiency).
  • chronic liver disease.
  • familial Med. fever (FMF): Melungeon (mixed American Indian, black & white...tri-racial) USA people...and others of Mediterranean ancestry...tend to run an elevated total WBC & a proportion may reflect "familial Mediterranean fever" [FMF...a cause of night sweats, fever, pains, chronic fatigue]).
  • chronic heavy metal poisoning.
  • chronic malnutrition (but less than 4% of "tired people" have a detectible vitamin deficiency).
  • occult malignant lymphoma and some other occult cancers.
  • brain stem compression (such as Chiari type I malformation...many of which have fibromyalgia-like symptoms).
  • hypopituitarism (tend very low blood pressure once adrenals are seriously effected)
  • temporal lobe epilepsy.
  • multiple sclerosis.
  • blood electrolyte disorders.
  • Addison's disease (adrenal gland insufficiency...tend to have very low blood pressure & some hyperpigmentation [especially in body creases] once adrenals are seriously effected).
  • myasthenia gravis.
  • [to my knowledge, mainstream medical practice has found no scientific evidence of chronic yeast or bacterial populations or environmental situations as actual causes...despite claims in the popular press].

References:

1. An excellent reference is "Palliative Management of Fatigue..." in JAMA, 17 January 2007, vol. 297(3):295-304.
2. Federal Gov.'s CDC arae on CFS [HERE].