I think adults with hyperphantasia can easily tell what's real and what's not, but I had a lot of trouble with it as a child. My parents were afraid I was hallucinating, so took me to see a child psychologist, but it turned out I was just pulling things from my extremely acute mind's eye into reality while awake like many people do while dreaming, and I hadn't figured out that didn't make them "real" in a way other people could see like it did in my dreams.

(I shudder to think how differently things could have gone if I had been misdiagnosed with a severe mental illness when all I actually have is an unusually powerful imaginative ability.)