[X] Answer truthfully. You'll tell everyone what you saw.
-[X] You were in a world where nothing around you was real. A world where maybe you aren't even real.
Honestly? This is the MOST realistic answer. Our protagonist saw death and was reborn, and while disapproval and betrayal by one you trust is bad, the thought that everything you are, everything you do and everything around you is a Lie, fake. Is a fear beyond the first two.
There's another reason why I didn't go with this... I actually know two people who have "psychotic episodes" where they experience that.
One of them has a seizure disorder; during and after the seizure, they become convinced that everything that they do is
fake. That they're acting, that they only fell down and puked because they
wanted to, even if there was no reason for them to want to and they were dreading it moments before they actually fell. Everyone, when they're having an episode, is just acting. Making up their lives for the drama, playing parts. That we are all just puppets to a mad god who is telling itself stories to itself to feel less lonely.
Then they recover, some twenty minutes later and they're back to normal.
The other person has a form of night terror on a daily basis. For the first hour they're awake, they're not sure if they're dreaming. In fact, they're frequently
still dreaming despite being wide awake. So they're not sure if any interaction they have with anyone is actually real, or if their brain made it up. They spend a good portion of each day sanity checking things, trying to make sure that what they're doing is grounded in fact.
In short, I have lived with two people with that fear, and I have seen how it can crumble a person. And it's common in France, specifically. There it tends to be a mild anxiety that you're expected to grow out of but a lot of people don't. It's comparable to that feeling that if you have limbs sticking out from the covers of your bed, something bad's going to happen, or a fear of the dark.
The fear that your life is a story, and the person telling it will finish whatever interesting part and you'll just... stop existing without dying. The fear that the storyteller will just close the book and walk away.