That one has bugged the crap out of me since I was a kid. How did I get to be "me?" How is it that "I" came to be in this body, in this time, but not someone else?
What, ultimately, does anything come from? When I was a little kid, growing up in a religious environment, this came out as "who are God's parents?" But even with a natural origin, how did anything come into existence? If energy cannot be created or destroyed, either god or the big bang involved a great deal of energy that had to come from somewhere.
Are things like spirits, OBEs, and other things real? Of course we can point out brain activity behind it all, but brain activity is behind every facet of our taking in and deciphering the world. Even things that most of us would regard as real, there is brain activity behind it.
What really is real? It's not like we have flawless perception and memory recall abilities, so to what extent can we trust our selves to distinguish what is real and what isn't? With dimensions we can't even perceive, just how much can we really trust our own senses?