Very sad.
I heard it was a dysecting of his aorta. In layman's terms, he developed an anurysm *weakness in the wall of his blood vessel*. The Aorta is the blood vessel coming out of the heart when it pumps blood to the body. Very hard to detect when a dysection is going on and very great blood loss all at once.
This is what my father died of this year. All mly dad complained about was it felt like his throat was closing.
John was way too young, very tragic.
j2bf