What Are the Symptoms of Chronic Fatigue Syndrome?

The hallmark symptoms include profound fatigue lasting six months or more that isn't improved by rest, post-exertional malaise (a crash in symptoms after physical or mental effort that's disproportionate to the activity), unrefreshing sleep, and often cognitive difficulties ('brain fog') and pain in muscles or joints. Some patients also experience lightheadedness on standing.

Because these symptoms overlap with autoimmune disease, thyroid dysfunction, sleep disorders, and mold or toxin exposure, a proper workup looks at all of these systems rather than treating fatigue as its own isolated diagnosis.