Thank you for the reply ali12. It certainly does sound a bit like the POTS thing. He says that sitting at his computer seems to be the worst thing for it. That is pretty grim on it's own because it's taking away yet another thing that he does to keep himself sane and happy.
He is going to ask to see a cardiovascular person so hopefully they will be able to get to the bottom of it.
He is pretty worried about having his driving licence taken away. We both live in rural areas and I don't drive so we would struggle to see each other if that happened. Do you drive?

Thank you for the video link LitLove. I am hoping it isn't that as his ekg was normal and not particularly slow or fast.

I have found out that there is a CRPS centre in Plymouth hospital so he will also be asking to be referred there.

Does anyone have any tips or lifestyle changes that might help him to feel better? He wants to get an exercise bike to try and maintain some fitness with gentle exercise, is this a good idea?
Thanks again everyone for the information and support.