Well, thank you for your advice, it makes a lot of sense. After three years not knowing what's wrong and struggling to get the dr to take me seriously, I have often felt it was something I had done wrong, my fault in some way, and so I've been searching to make it better myself by exercise, good diet, sleeping the right hours, etc etc. and even though it's still here despite trying all sort of exclusion diets, supplements and alternative therapies I still want to tell myself there must be something I can do to make it better!
Anacrusis, I had the same experience as you. Some friends of mine, who I think didn't believe I was making enough 'effort' encouraged me to go swimming. I had a feeling it would turn out bad and the same thing happened with me, I fainted in the pool and had to be carried out, otherwise I would have drowned.
So, all is easier said than done in practice, but I will give it the best go!