Hallucinations don’t belong wholly to the insane. They’ve also been associated with spiritual enlightenment and disease. They can be brought on by a simple fever or even the act of waking or falling asleep, when people have visions ranging from luminous blobs of color to beautifully detailed faces or terrifying ogres. Those who are bereaved may receive comforting “visits” from the departed. Ross Reynolds talks with noted writer and neurologist Dr. Oliver Sacks about hallucinations and his book by the same name.