The most common disorders manifesting predominantly as recent fatigue (lasting < 1 month) are Drug adverse effects Anemia Stress and / or depression The most common causes manifesting predominantly as prolonged fatigue (lasting 1 to 6 months) are Diabetes Hypothyroidism Sleep disturbances (eg, sleep apnea) Cancer The most common causes manifesting predominantly as chronic fatigue (lasting > 6 months) are Myalgic encephalomyelitis / systemic exertion intolerance disease / chronic fatigue syndrome Postviral fatigue syndrome Psychologic causes (eg, depression) Drugs Several factors commonly cause or contribute to a chief complaint of fatigue, usually prolonged or chronic fatigue (see table).