Centurionguard, I would struggle to describe your missing Mass in your situation as any sort of sin.
You had suffered shock at your brother’s collapse, an angina attack and you were in no fit state to be doing anything other than getting your bearings. Your individual circumstances at that time made you unwell, even if others’ reactions to such events might not have been the same. You were still in the midst of the emergency situation and emotional distress is more than enough of a reason in my eyes. Any priest worth his salt should say the same.
A similar thing happened to me a few years ago. One Saturday evening my elderly father took a nasty tumble and was in no fit shape to do anything - not even climb the stairs. I had to bring his bed down from the upstairs bedroom so he could rest and sleep. As a result I missed our normal vigil Mass. Then, the following morning, he was unable to move at all. So off we pootled in an ambulance and I missed Sunday morning Mass as well. Now I suppose that it was technically feasible for me to have left him in the hospital (which was in the next town) and sought out the local parish and possibly managed to find out the right times of their Sunday Masses, but I think my duty was to look after my father and ensure that his care was well managed. Nobody, not even my then parish priest, ever suggested I did anything wrong.
If someone is dying in front of us, or in danger of death, then we attend to them first. Our Sunday Mass obligation gives way to that and, in a sense, we give our most effective and visible loyalty to the teachings of Our Lord by doing so, since He commanded us to love others because of our love for God.