Short answers, pulled from the story.
Sir Thomas Browne introduced the word hallucination into the English language in 1646. He derived the term from the Latin word alucinari, which means to wander in the mind. Browne defined the phenomenon as a depraved vision that receives its objects erroneously.
An estimated 9.6% of the general population experiences auditory hallucinations in their lifetime. These hallucinations often take the form of voices that speak to the subject or comment on their actions. Research indicates that 55% of these auditory hallucinations are malicious in content.
Charles Bonnet syndrome is a condition affecting partially or severely sight-impaired individuals who experience complex visual hallucinations. These formed hallucinations are clear and lifelike, often causing the subject to fear they are losing their minds. The hallucinations may persist for months or years depending on the speed of eye deterioration.
Tactile hallucinations known as formication create the sensation of insects crawling underneath the skin and are frequently associated with prolonged cocaine use. This sensation also occurs during normal hormonal changes like menopause. The neurological basis for these sensations lies in the postcentral gyrus and the posterior frontal lobe.
Hypnagogic hallucinations occur as one is falling asleep while hypnopompic hallucinations happen when one is waking up. Surveys suggest that 37% of respondents experience these hallucinations twice a week while remaining aware of the true nature of the images. These events are sometimes associated with narcolepsy or brainstem abnormalities yet can occur in healthy individuals.
A 2015 review of 55 publications from 1962 to 2014 found that 16 to 28.6% of those experiencing hallucinations report at least some religious content. This suggests that hallucinations are not merely random noise but can be deeply tied to the subject's cultural and spiritual framework. In 90% of cases of psychosis, a visual hallucination occurs in combination with another sensory modality.