Chronic fatigue syndrome and fibromyalgia are similar conditions with some key differences. They’re both considered central sensitivity syndromes, with both involving fatigue, pain, and cognitive dysfunction.
Chronic fatigue syndrome (also called myalgic encephalomyelitis or ME/CFS) is more often tied to immune-system abnormalities than fibromyalgia. And fibromyalgia is generally more painful than ME/CFS.
But both conditions affect multiple systems in the body. They’re sometimes referred to as neuroimmune or neuroendocrineimmune disorders to reflect that.