ultramarina - I wish that would work for her! Sadly, she's an absolute skeptic and it's rare that she'll believe something just because an adult says it (if anything we're always completely exhausted because she wants us to prove everything! A great trait to have, in general, but oh man is it tiring!).
Ha. Oh, mine is this way, too. However, seeing multiple experts stating the same thing over and over is at least vaguely helpful. She still comes back with, "BUt what if they're wrong???", though.
Not to hijack, but whereas DD9 fixates on "what if" scenarios (death, sun burning out) as well as being freaked out by infinity and the size of the universe, DS5's bedtime angst episodes focus on feelings of great emotion about past events that were enjoyed but are over--vacations, visits with family, Christmas, etc. He has trouble with the fact that these things are over and feels melancholy about the past being past. He seems to worry that things will not be "fun" again. He also really misses family members who live far away and always struggles after we part from them.
This is quite different than DD's issues. He also will sort of perseverate and say he "can't get things out of his mind," even though he wants to. Anyone else have something like this?
I will share what we do with him, though: we have a list of fun things we do regularly by the bed for him to look at with a flashlight and think about (such as going swimming, going to a movie, playdates with friends, etc). This helps him think positively about the future.