https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1293107/pdf/jrsocmed00127-0072.pdf
Chronic fatigue syndrome (CFS)
(a) A syndrome characterized by fatigue as the principal symptom.
(b) A syndrome of definite onset that is not life long.
(c) The
fatigue is
severe, disabling, and affects physical and mental functioning.
(d) The symptom of fatigue should have been present for a minimum of 6 months during which it was present for more than 50% of the time.
(e) Other symptoms
may be present, particularly myalgia, mood and sleep disturbance.
(f) Certain patients should be excluded from the definition.
They include:
(i)
Patients with established medical conditions known to produce chronic fatigue (eg severe anaemia). Such patients should be excluded whether the medical condition is diagnosed at presentation or only subsequently. All patients should have a history and physical examination performed by a competent physician.
(ii) Patients with a current diagnosis of schizophrenia, manic depressive illness, substance abuse, eating disorder or proven organic brain disease. Other psychiatric disorders (including depressive illness, anxiety disorders, and hyperventilation syndrome) are not necessarily reasons for exclusion.