Do you have allergies? My a.m. cortisol results were very high, and it is because of allergies. (One of cortisol's functions is to reduce the amount of histamine in your body) You can still have adrenal fatigue with a high a.m. cortisol, especially if your p.m. results are way off. I have also heard that when your thyroid isn't functioning correctly, the adrenals often try to make up for this. Cortisol can be converted to other body hormones. This will eventually lead to adrenal fatigue.
Cushing's produces some very obvious physical symptoms and body changes. I think you would know if you had it. The endocrinologist would suspect it right away.