Anyway, how do we know he wasn't lying, lying is pretty easy to do nowadays, people fall for all sort of things.
He certainly wasn't lying about what happened to his brain to put him in the coma and his miraculous recovery from it. He certainly didn't plan out this elaborate hoax for months and then suddenly fall ill with a deadly disease that rendered him in a coma for a week. A disease he should never have recovered from, just so, "if" he miraculously survived he could pull of an elaborate hoax about what happened.
A guy who taught neurosurgery at Harvard for 17 years and no longer believed in God and then suddenly and inexplicably awakens from a coma doesn't usually develop an incredibly detailed and elaborate hoax about things that happened, especially when he knew that sharing his experiences would surely mean he would be laughed at and ridiculed by the vast majority of his peers.