John, I'm not a psychologist, but I sometimes pretend to be one at work.
I don't understanding the horrible fear you felt after your bigfoot encounter. It's not like bigfoot waved a hairy paw/hand in your direction, beams of light shot out of its eyes, and you were suddenly and involuntarily thrown down in a fetal position. From what you've described, it was just some critter sitting there, minding its business, munching on some bushes. Granted, it wasn't an animal you recognized or expected, but it made no threatening gestures in your direction, no roars of rage, no beating of the chest, nothing. Yet you have obviously been deeply affected by the events that day.
I guess I'm scratching my head wondering why? What is it that you found so terrifying about the incident?
RayG