Hallucinations, for most people, imply madness. But there are many different types of non-psychotic hallucination caused by various illnesses or injuries, by intoxication--even, for many people, by falling sleep. From the elementary geometrical shapes that we see when we rub our eyes to the complex swirls and blind spots and zigzags of a visual migraine, hallucination takes many forms. At a higher level, hallucinations associated with the altered states of consciousness that may come with sensory deprivation or certain brain disorders can lead to religious epiphanies or conversions. Drawing on a wealth of clinical examples from his own patients as well as historical and literary descriptions, Oliver Sacks investigates the fundamental differences and similarities of these many sorts of hallucinations, what they say about the organization and structure of our brains, how they have influenced every culture's folklore and art, and why the potential for hallucination is present in us all.
An Amazon.com Best Book 
“Absorbing…. His compassion for his patients and his own philosophical outlook turn what might have been clinical case studies into humanely written short stories, animated as much by an intuitive appreciation of the human condition as by scientific understanding.”
—Michiko Kakutani, The New York Times Book Review
“[I]t is impossible not to get sucked in by the sheer enthusiasm with which he tackles his subject, the breadth of knowledge and research he brings to it, and the quirky charm he unleashes on nearly every page.”
“Sacks triumphs. Not just in the clarity with which he teaches us about the obscure phenomenology of the human brain, but in the light his writing casts on even our most ordinary experiences.”
—The Telegraph (4/5 stars)
“[Sacks is a] master at bridging the arts and the sciences…. Fascinating book…. Written with both grace and erudition, Hallucinations taps into the mysteries of the human brain in a way calculated to appeal to both the scientist and general reader with a questing mind.”
"Oliver Sacks is our greatest chronicler of people with unusual neurological and sensory disabilities and experiences."
—The Globe and Mail
"With his trademark mix of evocative description, probing curiosity, and warm empathy, Sacks once again draws back the curtain on the mind's improbable workings."
—Publishers Weekly (starred review)
"Oliver Sacks...gets trippy."
—Quill & Quire