I think you need to get a good doctor. I found a list of 3 doctors who could treat your problem possibly. I definitely think you have an adrenal/thyroid combination. The extreme hypothyroid you have is causing depersonalization/brain fog, and I know this because I have the same thing.
This list of doctors can treat all different kinds of thyroid problems, and will probably have some experience with adrenals. The adrenals going out is what causes hypothyroidism in the first place, so fixing the adrenals by raising cortisol should be the first step usually. This is the hard part though, as it can be done by either transdermal pregnenolone cream, transdermal progesterone, hydrocortisone pills, or even using ssri's (antidepressants) to raise your own cortisol production.