Hi Mabel,
Sorry to hear about your partners problems. There is nothing worse than KNOWING there is something wrong, but not having a diagnosis. I really hope you find a good doctor soon, I know just how difficult that is and how time consuming it is in the UK.
Just wondering, has your partner ever heard of anything called Postural Orthostatic Tacharcadia Syndrome (POTS). I have both RSD and POTS and a lot of the symptoms I have sound like what your partner is experiencing. The two also often go hand in hand, especially if he is hypermobile.
The main symptoms of POTS I get are chest pains, feels as though my heart is racing. I also black out, to the point where I used to faint around 20 times a day. Other symptoms are inability to control blood pressure (mine fluctuates a lot and is either extremely high or extremely low), inability to regulate sweating, an increase in heart rate upon standing / sitting too long (has to be by 20BPM to be POTS) and migraines on a daily basis.
If you want any further info let me know. I'm happy to help. One thing you could try is getting a BP monitor and keep check on his blood pressure and also his pulse upon standing. I'm under a cardiologist for it and if it is something you feel he may have i'd urge you to see a different one if possible.
Wishing you both well
Alison