I haven't tried isocort myself, but I am on an adrenal complex which definitely has helped. My ND who specializes in adrenal fatigue says that he gets the best results with adrenal glandulars. The crashing you speak of is par for the course with AF, sometimes I'll catch a glimpse of normalcy, taking 2 steps forward and then 3 steps back. Dr. Lam says that adrenal fatigue is like running a marathon with hills and downgrades, easy parts and not so easy parts. The point being that it is a long road back to recovery and you have to be patient. He says that depending on your case it may take anywhere from 3 months to 3 years to fully recover. I myself have been dealing with AF for a year and a half but only diagnosed and treating it for 8 months now. I have made great progress but still have a ways to go yet. The endocrine system is a very delicate interconnected network with loops and feed back messages that all get scrambled even if one part is off by a bit.
The important thing to realize is that you are not going crazy and it is not in your head! Because this is a physical ailment, I like to tell myself that I am injured NOT sick. What I have found as I get better is that I will have 2-3 good days a then 2-3 bad days. Before it was ALL bad with no hope of happiness making me dread getting out of bed in the morning because I didn't want to face another day of torture (even though all I was doing was getting out of bed and then moving over to the couch!). Eventually the good will start to out number the bad and you'll be on your way.
Through out this ordeal I have learned to slow down, let my anger go, appreciate nature and most of all, enjoy the small moments in life- because that's all that really matters. I have gone from an egomaniacal hot head, who thought that the world owed him something, to being a patient, loving, compassionate human being. This has been the silver lining in the dark cloud... I encourage you to find your own. There is a lesson to be learned in all of this that is personal to you and you only:
"If God wants our attention, first she whispers, then she speaks and then she shouts."
I wish I had of listened when she was whispering. ; )