I do not think a small difference in the way his dental visit was described by 2 sources is really all that great a problem. People remember things differently, and they describe them differently even when both parties witness the same things directly in person. Elvis would not tolerate pain of any kind, and because he was so use to painkillers...any pain he had probably was seen as severe by him-so for him to ask for pain meds is not really a revelation.
As far as the pain of heart attack, many people do very strenous activities such as raquetball .....and then have massive heart attacks, Bing Crosby dropped dead after playing 18holes of golf from a massive heart attack-he had not mentioned he was having pain, Ross Martin died after a couple sets of tennis, he had been having mild pain in his shoulder and arm-that he thought was a muscle problem (since he had a history of heart trouble he should have paid closer attention) author Rod Serling had been jogging when he was struck with a fatal heart attack, my own grandfather died just sitting in his chair-but had been complaining for a few days of left shoulder pain.........heart attacks are much more complex than people realise-some people have them and do not even know they have, healthy people are killed by heart attacks each year who never had a hint of heart problems, and some people have warning signs for months but do not see the connection. There is no textbook heart attack-it hits everyone in a different way.