According to Dr. James L. Wilson, adrenal fatigue is often associated with CFS, but commonly unrecognized.
Adrenal fatigue causes a lower cortisol level (energy metabolism), and affects aldosterone (sodium, magnesium, and potassium balances). AF may also lead to hypoglycemia (low blood sugar).
Cortisol has a circadian rhythm.
Cortisol should be high in the morning and gradually decline. It normally takes a dip between 3 PM and 5 PM. The level is strongly affected by meals and snacks which cause a burst of cortisol.
People with adrenal fatigue have lower cortisol levels, and the levels may be erratic compared to normal.
Higher sustained cortisol levels and improved adrenal health can be achieved by frequent small meals (every 2 hours). In addition, supplements like glandular extracts, vitamin C, bioflavonoids, and magnesium can be helpful.
Personally, for adrenal fatigue and hypoglycemia, I keep sugar and sea salt near me in case I need a boost at night. In the daytime, I take extra salt to address the aldosterone component.
For a good explanation, I recommend the book by James Wilson, N.D., D.C., Ph.D., who wrote "Adrenal Fatigue, The 21st Century Stress Syndrome."