Question

Why people sometimes have hallucinations? How it occurs?

Answer 1

We could write an entire term paper, if we wanted to give every reason for why people have hallucinations.

Hallucinations can happen for many reasons.
Mental disorders (like schizophrenia), neurological disorders (like Parkinson's disease), drugs, fatigue, migraines, etc.

Some hallucinations are actually normal. That's something not everyone knows.

There's a certain kind of hallucination called a "hypnagogic" hallucination.
When these hallucinations happen, they tend to happen right before we fall asleep, as we're starting to get drowsy.
We might start start seeing images, or hearing voices. Many people actually experience hypnagogic hallucinations.

Sigmund Freud explained the reason for why hallucinations happen with unconscious thoughts and desires. Wishes that we aren't consciously aware of.

And other scientists believe that there are two neurotransmitters that play an important role in hallucinations: dopamine, and glutamate.
As for exactly how they play a role, I've got no idea.

Do you know anything about hallucinations?