Personally, I never knew I was hallucinating until my counselor saw me responding to what wasn’t there in his office. I didn’t know before that they weren’t real. My psychiatrist said you can learn to tell what is a hallucination. I’m trying to learn.
I get either the type that takes place in my head or the type that manifests outside my body, but the second group is always see through like a hologram, so it’s easy to tell it apart from a real person.
Whispers are the only things that have caused me to second guess myself. Luckily most people in my family never whisper.