Deane, When I worked in medicine, I only saw one case of Xyphoid in 15 years, and at that time, which I believe is true today, no one really knew what the cause or trigger mechanism was that produced the pain. The one case I saw that patient was in extreme pain, however, it subsided after just a couple hours and he drove home as if nothing had happened. Just another one of those mysterious pains that never gets diagnosed. Look at the bright side, at least there was someone there that could diagnose the problem, and enlighten you about your heart condition.
All the best,
Gary
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K+E=W (Knowledge Plus Experience = Wisdom.)