I have low cortisol levels, though not addison disease. how may they treat it?

Many options: I don't know how your docs may treat but I'd advise adrenal supporting herbs like Ashwagandha, Rhodiola & Cordyceps, reducing stress (both physical & emotional), healthy low-glycemic diet, adequate rest & meditation. Treat any infections (including chronic low-grade ones) & avoid allergens/allergenic foods (often undiagnosed). Consider adrenal glandular extracts. See http://www.adrenalfatigue.org/