How does cfs relate specifically to fibromyalgia?

They are overlapping: Although cfs and fibromyalgia have distinct criteria that needs to be fulfilled, they are often diagnosed together. Fatigue is a common feature with cfs and in fibromyalgia.. With the later we more often see a significant sleep disturbance which is a primary contributor to the fatigue. Although pain is certainly a feature of both, but with a positive tender point exam is confirmatory with fibro.

Fatigue and fibro: First of all there any of number of causes of fatigue - from apnea, hormonal deficiencies, low blood pressure, anemia, vitamin deficiencies, depression, etc. Not infrequently non-restorative sleep or chronically marginal blood pressure can be undiagnosed causes. Shallow breathing and/or anxiety can also be catalysts. Medications including antidepressants and narcotics can worsen or even cause.