Hello What
I understand you feel deeply distressed and anxious. Calm down. Deal with the health issue as it happens, everything else can be addressed in good time.
It's possible he's having some sort of heart complaint, you need to contact the doctor or a hospital if he has all the signs of a heart attack. Look on NHS direct. Plenty of people have silent heart attacks which, thankfully, do very little damage these days (comparatively) and sometimes are even not noticed as having happened until months later.
But really, I would guess that this is anxiety related. People who have affairs and have their relationships spiral as a result are in a constant state of stress and anxiety and panic attacks and palpitations are normal. Your partner was and still is, almost certainly, being unfaithful. You need to accept this, sit and breathe and let it sink in as a fact.
You then need to realise that it has never been addressed properly. He has not done any of the things that would constitute trying to rebuilt the levels of trust that he tore down, and you have been the one to make effort. This makes things worse rather than better as the lesson learned by him is there are no consequences except you are nicer to him. It makes things worse for you because you feel insecure and upset all the time and ultimately worthless and resentful.
Your relationship is clearly unequal and has huge problems with fear and lack of communication. The counselling is the right idea but you are in a dreadful situation and clearly desperate.
Deal with the health issues, coldly if necessary. 'Caring' for him is unnecessary as I suspect this is all related to the pressure and atmosphere his infidelity and you capitulation has built up in the home.
If you are saying any emotional talk is impossible with him, why on earth do you imagine continuing in a relationship with him at all is feasible? It just isn't. Why do you so need to be 'accepted by him' when he treating you worse than a doormat? Step back from this and consider what you'd tell a good friend who was going through this.
You seem cowed and caught in an unhealthy dominated situation where you can't even ask him in response to a text you've received, unsolicited, what the hell is going on. This is a reasonable question, hell a logical demand. This seems like an affair is reaching its head, a jealous or troublesome OW is stirring and you are clearly going out of your mind and he is breaking down physically. If you truly cannot confront him about this then you need to leave the house and leave a letter when he is out explaining that the situation is intolerable and go and stay with someone, anyone.
I mean this all very seriously, OP, and I sympathise hugely, but this cannot go on. You need to take charge and address this terrible terrible behaviour he has visited on you, or I fear your life will be destroyed, one way or the other.