Sorry @Equallength I was too late to offer any advice - but it would have been "he needs to go to A&E". My other bit of advice is for any time there appears to be a medical problem:
It doesn't matter how well someone unknown on here (or anywhere else for that matter), describes the symptoms and/or a condition the questioner is asking about, or how emphatic they seem when giving you a diagnosis, no qualified medic would say that it was such and such - they might suggest it could be such and such - but they would follow that up with that it has to be seen by a Dr - and in your DH's case, today - whether that be the patients own GP, a walk in centre, minor injuries, or A&E proper.
With your DH's previous history OP my suggestion would have been either he needed to see his GP today (yesterday), or A&E, no messing about with anything else, it would have just been wasting time. However, your DH eventually went to A&E, which is great, and even if it turned out to be something really simple (I hope it did), I still believe that it was the right thing to do in these circumstances.
Also, and sorry I know this is obvious anyway, if one of the online "experts" in Mumsnet were right in their diagnosis this time, it does not mean that they, or anyone else (including me) will be correct another time. I think that you did the right thing coming on here for advice, and that is for the simple reason that I am yet to see someone on here seeking advice for an acute and serious sounding medical problem, and them being told by the majority "not to see a Dr the same day".
Unfortunately OP, as you have probably already realised, if you read many acute medical posts on here you will almost certainly have seen the advice that "unless someone's head is hanging on by only a blood vessel, or they have actually stopped breathing, don't waste A&E's time, and whatever else they do or don't do, they must never call an ambulance! Ok, I admit that I may be exaggerating a little bit, but some people do get rather carried away when thinking A&E visits are unnecessary, and that hardly anyone should ever call an ambulance.
Sadly, I do know that some people are idiotic enough to call an ambulance because they have a spot on their nose that is hurting, or because they have missed the last bus home, which is 15 miles away, and they can't afford a taxi, but I doubt very much that we get many people like that on Mumsnet? Ambulance control itself will do a mini triage, and decide how urgent someone needs an ambulance, and they will advise some people that they will be waiting 12 hours for an ambulance so they might prefer to make their own way to hospital, or even to see their own GP.
@Equallength if you haven't already while I have been typing this, please let us know how your DH is 💐