What causes mental illness?
Hallucinating due to mental illness is usually associated with schizophrenia, schizoaffective, psychotic mania or depression. The cause is genetic but it is thought to typically takes some stressful life event to trigger the illness. Occasionally, drug use is the trigger. There are meds that can control the illness for most. All are progressive (get worse) illnesses when left unmedicated, so treatment sooner with med compliance leads to much higher functioning. Btw, these diseases are thought to be genetic, so if you did not inherit the genes, you won't get them.
Is it possible to fake mental illness in order to claim an insanity defense against a crime?
Anything's possible. A person can try to claim insanity, but in the US insanity defenses are incredibly hard to pull off. They only work about one-third of the time, and you pretty much have to have a long history of serious mental illness, including psychosis. There are many, many instances of people who are crazy by any imaginable standard but not legally insane.There is, for instance, a schizophrenic serial killer in California named Herb Mullin, who murdered people because he thought God would send earthquakes to tear the whole state apart if he didn't. Read about him here: The Die Song ExplainedYou see, the thing is, people get together, say, in the White House. People like to sing the die song, you know, people like to sing the die song. If I am president of my class when I graduate from high school, I can tell two, possibly three young male Homo sapiens to die. I can sing that song to them and they'll have to kill themselves or be killed — an automobile accident, a knifing, a gunshot wound. You ask me why this is? And I say, well, they have to do that in order to protect the ground from an earthquake, because all of the other people in the community had been dying all year long, and my class, we have to chip in so to speak to the darkness, we have to die also. And people would rather sing the die song than murder.And this guy was found to be legally sane and responsible for his actions.So, well, anything's possible, but it's not terribly likely that a person can fake mental illness well enough to get declared legally insane. I might also note here that people who are declared criminally insane tend to spend more time in secure mental hospitals than they would have in jail if they'd been declared sane and guilty. In a book on that subject I read about one man who was shut up in a mental hospital for years after he was declared insane when the police arrested him for turnstile jumping.
Can drug abuse be misdiagnosed as mental illness?
Yes. Drug dependence, intoxications and withdrawals can cause symptoms that can be indistinguishable from schizophrenia, schizoaffective disorder and bipolar disorder. They usually always do a drug screen to rule out the possibility that drugs/alcohol are causing the symptoms. Also, since patients are not always completely honest about their history of drug use they may interview family members and others close to the patient. The correct diagnosis usually becomes clear when the person is off drugs. After a significant time of abstinence (at least one month) if the person is still experiencing symptoms then it's likely they're suffering from a non-substance-induced psychosis.