I was thinking along the lines of what I know about neurological conditions and the susceptibility to have a hallucination, autitory, olfactory, and visual. Migraine sufferers sometimes report an aura. An injured brain of any level can lead to a hallucination. I guess from my viewing from a neurological perspective is an underlying understanding that one can also have full function of self despite hearing, seeing or smelling something that is not part and parcel of present, physical reality.
For me, if I lack enough sleep, I'll see shadows. Sounds can seem louder. Just part of the spotted matter on my brain. I make sleep a priority, as a result.