I know exactly how you feel but I have suffered a head and neck injury, which left me with all the problems you are describing. Have you ever had such an injury ? A couple of years later I paid for a referral to the ‘autonomic unit’ in London, after getting nowhere with the NHS. They diagnosed me with a few things - features of POTS, peripheral vestibular dysfunction, mild radiculopathy and small fibre neuropathy, namely. I had intermittent symptoms of other things like swallowing issues but, if you’re not symptomatic at the time of testing, diagnoses for the cause of these seem impossible to get.
Going back to you though, I wonder, could the spin out be contributed to by ‘lack of sufficient blood delivery to the brain’, do you think? i.e. Does sitting down resolve it ? Or do you think it could be ‘information overload to the brain’ - I totally get that ?
I use a powerchair, so there’s little exertion when I’m out and about but, even so and with someone to carry the shopping, it still absolutely drains me, I don’t get it, how can I be more active at home and yet still fresher than after an hours shopping, I wonder if it’s something to do with the repetitive head movement.