You were experiencing acute adrenal crisis from a lack of cortisol.
If you take prednisone long enough, especially high doses, your adrenal glands are suppressed. You have to taper off slowly in order to give your adrenals time to resume normal function.
Despite knowing about this hazard I’ve managed to blunder into adrenal shock a couple of times because I absolutely hate prednisone’s side effects and I try to rush the taper.
Yeah it was awful- My doc was shocked when i said i stopped the steroids- he asked if i tapered, i said “No- was i supposed to?” I was on it kinda long term due to a condition- i was feeling better and wanted to be off them and took it upon myself to stop instead of doing the right thing and asking doc —
I’ve only ever had a headache like that one other time when i was out in sun all day- long drive home head started to hurt- and by time i got home, it was so bad i threw up from it then too-
If i ever have to take prednisone again- I will go strictly by the book on tapering