Delusional embellishment. My experience with evangelicals is that the testimony gets more intense as time goes on. The glassy-eyed oohs and aahs that the teller gets from fellow believers reinforces the narrative. I think many come to believe the story that they tell.
I do not believe that habitual liars begin to believe their embellished, or completely made up, stories. Not for one second. They are just very good liars.
Maybe he tried to perform neurosurgery on himself.