What happens to your brain when you hallucinate?
When you hallucinate, most parts of your brain become extra active; 30% more active than when you're awake. For example, visual, motor, emotional and memory centers, they all increase in activity. Meanwhile, prefrontal cortex, the CEO of the brain so to speak, good, rational, logical thinking part, it gets shut off.
That's why you see things, why you have motor kinesthetic activity, why things feel so emotional, but also why things seem illogical and irrational.