hallucinations demons or schizophrenia

How do we know if someone is seeing something spiritual or not? I saw this video of a schizophrenic describing his episodes where he will see shadow people for hours at a time, he can taste stuff that happens in his hallucinations (spiders running down into his stomach), hear and see bugs crawling from everywhere. My first thought is that he is demon possessed but I have read that the Orthodox church sees schizophrenia as a legit mental health disorder. Is it possible that modern medicine can prescribe you mental disorders while all along it is something spiritual? This is confusing me because there are many spiritual testimonies that confirm what they see by activating more than one sense. If you all could share your spiritual experiences maybe that would help so I can understand the differences as well. Or if there is a source that addresses this because I have found nothing of the sort so far.