I could really only tell if it just didn't look real at all. At the first onset, I was absolutely convinced that my toes were frozen. They even 'felt' cold to me. No one seemed to be able to convince me they weren't really like that. After I was diagnosed, I still didn't believe they had schizophrenia and thought they 'got it wrong'. It took a while to decide that it wasn't actually hypothermia, over a year after I left the first mental ward. When I relapsed again (after quitting medication dumbly), I accepted that I actually had it and it was easier to decide that what I was seeing was just my brain playing a trick on me.

Hallucinations weren't constant but my delusions were, especially about being 'sick with hypothermia'. It didn't really 'pass in front' but more like 'obstructed my vision' from seeing the real thing. My toes could move out of my view but I was still convinced they were purple even if I wasn't looking, then I would pull my socks off or whatever and they would just look purple. Some hallucinations that were reliant on other things, like watching TV and seeing it 'leaking', I could just walk away from. I would think that the biggest factor for knowing they're not real is admitting that you're schizophrenic and not feeding into the delusions. You still struggle with it even though you know what's going on, I could ignore the hallucinations but my mood was all over the place and I didn't have much control over my own thoughts. I would often just lay in bed at the mental ward in the fetal position with blankets over my head and my eyes shut so that 'nothing could bother me' such as hallucinations. I would try to 'think about nothing' so that I could fall asleep too and not set off any hallucinations but you never really knew when they were going to happen.