Severe Fatigue of an unknown cause lasting for more than one month (medically referred to as “idiopathic fatigue”) is a condition in which the sole symptom is fatigue that is not made better by rest.
If the condition lasts more than a month, it is referred to as “chronic severe fatigue”. If the condition lasts at least six months but does not meet the criteria of ME/CFS, it is termed “idiopathic chronic fatigue”.
Labels aside, It is estimated that as much as 4% of the population suffers from severe fatigue. As widespread as severe fatigue is, it is a complex task to get at the root of its causes and to distinguish between the various types of fatigue.
While depression and stress are common causes of fatigue, there are endless possible physical causes. It is critical, therefore, to distinguish between body and mind disorders, as the source of the fatigue. This can be an extremely challenging task for any physician.
In some cases, when a medical explanation for severe fatigue is elusive, patients are told there is nothing wrong with them.
In other instances, people who complain of fatigue are often misdiagnosed with depression when they may be actually suffering from an endocrine disorder such as a thyroid condition called hypothyroidism which can be dramatically resolved with the appropriate treatment.
Those suffering severe fatigue not made better by rest require a careful and comprehensive evaluation by experienced clinicians.
More detailed information on severe fatigue may be found in the book Your Symptoms are Real: What to Do When the Doctor Says Nothing is Wrong by Dr. Benjamin H. Natelson.