Cold-turkey steroid stopping is not advised... depending on the dose, yes, it can be quite horrible and even dangerous.
Some people can have the adrenals atrophy with long term use - some people it triggers other things.
I took Flovent for 10 years to treat asthma but I came off it 3 years ago; I experienced my first "adrenal crisis" or whatever it's called after I quit the Flovent. Sudden vomiting, painful stomach pangs but at the time, I did not know what to do so I just did nothing and pushed through it. I was told afterwards I was lucky to have survived it but maybe that person was being dramatic? I don't know. I've been okay since then but my adrenals are really struggling and hoping not to experience that again.
AF is not a medical diagnosis - it is probably a combination of things...
AI however is a medical diagnosis but you would likely lose weight, not gain. The higher evening cortisol is more indicative of Cushing's - where you would gain rather than low cortisol and there is a lot of overlap of symptoms (I know this since I had Cushing's and my adrenals were removed to resolve it).
Most endos don't know how to treat it - or PCPs - so you have to find a good one. But if you think you have AF and take steroids well, it will just make you worse.