First, see the Wiki article on schizophrenia. Here's some highlights;
Schizophrenia (/ˌskɪtsɵˈfrɛniə/ or /ˌskɪtsɵˈfriːniə/) is a mental disorder often featuring abnormal social behavior and problems distinguishing what is real from what is not. Common symptoms include distress, hearing voices or noises that are not there, inattention, confused or unclear thinking, inactivity, and reduced emotional expression and social engagement.
The disorder is thought to mainly affect the ability to think, but it also usually contributes to chronic problems with behavior and emotion. People with schizophrenia are likely to have additional conditions, including major depression and anxiety disorders; the lifetime occurrence of substance use disorder is almost 50%. Social problems, such as long-term unemployment, poverty, and homelessness are common.
**Individuals with schizophrenia may experience hallucinations (most reported are hearing voices), delusions (often bizarre or persecutory in nature), and disorganized thinking and speech.
Today, if someone claimed to be hearing God's voice, we would likely point them to a doctor so they can get treatment. However, the authors of the Bible considered it perfectly normal for individuals to hear God's voice, see visions, etc. Hearing voices and seeing hallucinations are clear symptoms of schizophrenia. So when I read the Bible, I wonder how many of its prophets and apostles were actually schizophrenic rather than genuinely hearing from God.
Paul, out of all the Bible's authors, could easily have been schizophrenic. His conversion was the result of seeing a light and hearing Jesus' voice.
Is there any good reason why I shouldn't believe people like Paul and the other prophets and apostles in the Bible had undiagnosed mental health problems rather than that they were genuinely hearing from God?