I also tend to be distrustful of these words. I think the message I'm looking for is something closer to "You're safe with me," but those words would also not feel safe. Perhaps if a lucid explanation followed as to why I was safe, that would work.
I am autistic, lol.
Focusing on small objects in my environment tends to help a bit as a "grounding" technique.
Too distant to seem "real." Potentially immersive, yes. Maybe "real, but not for me"? Like tuning into a signal about things happening to people in other places and times. That's amazing, but doesn't put me "in" an environment. It's the sensory world I'm trying to connect with. But as expectations are low while reading a book, I don't tend to get an upsetting sense of de-realization while doing it. I mean, if nothing else, I'm less focused on this physical world feeling distant, and again, not expecting the book world to immerse me fully in a 3-dimensional universe. So I tend to be pleased with how effective it actually is.