Shit mate, they are horrible.

I have only suffered them once - for a two month period -ish - when my Dad was dying and was a very shit place in time for me.

I only pinned down what was causing them in retrospect - not at the time.

I can't offer you any advice, sorry, but this might help you pin down any underlying causes...?
(maybe, I dunno, just offering what I know from my own experience).