The only visual hallucination was seeing my wife just after she'd died. I've been told that's a fairly common experience. I've experienced the very occasional olfactory hallucination,but ask me to voluntarily imagine the smell of something and I can't do it.  As a whole I don't experience hallucinations very much. The most frequent are functional hallucinations.What sound like voices as the washing machine is running. Hearing what sound like voices when the toilet is flushed. For many it happens with the sound of a fan.