Does a post-game unnerve anybody else? You're stuck in an unchanging world with nothing to do. Think of it like this;

Imagine continuing on with your life after doing all your goals, you've tried all you wanted to, you don't have any goals now, nothing new happens, nobody dies, nobody is born, humanity doesn't advance or regress and this goes on forever. The world is still from the moment you did your goals.
Wouldn't this be nightmare?

When I beat Red in Pokemon Gold as a kid, i had this weird feeling, of being lost and not knowing what else is left for me in this game. Sure I could do the pokedex but nothing new is going to happen other than some stuff when i finish it and even then what do I do next? I'm alone, stuck in this place, that I spent ages on as a kid, grew to love and am now making up shit to entertain myself with now.