Fatigue is a frequently encountered symptom in Social Security disability claims. Fatigue can be a component of many conditions, including fibromyalgia and Lyme disease. Fatigue is often secondary to conditions involving chronic pain, because it is exhausting to be in pain all the time. Fatigue can also be secondary to severe depression. And of course, there is chronic fatigue syndrome.
Fatigue can certainly be a disabling symptom, and a record of your fatigue and its effects can help to establish your disability claim. However, your fatigue must be documented to strengthen your claim. Unfortunately, fatigue is often not well documented in the medical record.
So consider keeping a journal. And tell your doctor about your fatigue, and how it limits your ability to function. Ideally, your treating physician will complete a medical source statement setting forth your functional limitations, including those due to fatigue. That is the best evidence of all.