Sorry to hear you are not feeling well jgr.
This happened to me about ten years ago, I was absolutely fine one minute - in a pub at the bar getting a drink - and then I just came over feeling very weird and fainted. Felt awful for a couple of days afterwards - like pressure on the back of my head/neck area.
Had loads of tests but nothing showed up - I ended up putting it down to menopause (early stages then).
Even now I cannot stand in a queue in shops as I start to feel dizzy and faint and I always use a trolley in a supermarket, even if only buying a few things, just to give me something to hang onto.
I am sur