if you genuinely feel as though you are not ready to handle what you are experiencing, then obviously the trip will manifest it as such, and bring your subconscious worries and fears right to the surface.
in that trip you linked to, OP, that member had been using it often and in larger doses than "average".
he had been getting constant recurring trip themes, WHICH HE IGNORED.
he knew he was doing too much, too often, and he was directly and actively interacting with what he percieved as negative and evil entities and energies.
dont mean to sound harsh, but IMO he got what was coming to him.
play with fire and you WILL get burned at some point. this isnt acid, as someone pointed out already,
this is the strongest stuff known to man.
as someone else has pointed out before, too-
"in the depth of a hellish DMT experience, you cant simply close your eyes and tell yourself 'this isnt real, this isnt happening' as DMT directly affects the parts of the mind that deal with "real" and sense of reality and self"
tele said it; ANYTHING is possible on DMT. you make your experience partially.
if you're not reckless and dosing high and often, i dont think you have anything to worry about. but who knows.
either way i wouldnt go playing with any ouija boards.