It might come as a surprise to learn that Oliver Sacks' writing career, characterized by sensitivity and compassion, began in a revelatory stupor.

Sacks, the neurologist famous for explaining medical mysteries in "The Man Who Mistook His Wife for a Hat," "Awakenings" and other books, came upon the idea of writing medical narratives while under the influence of amphetamines in 1967. His personal story is one of many that make up his latest book, "Hallucinations," in which he again assumes the role he has perfected over many years: that of a layperson's medical guide to the brain.

In his new book, Sacks seeks to negate the stigma and misunderstanding that surround hallucinations. Hallucinations often are associated with psychosis and dangerous delusion, but Sacks explains that a wide range of medical conditions can result in seeing, hearing or even smelling things that are not there; hallucinations can be brought on by medications, epilepsy and sleep disorders.

Hallucinations can consist of simple lines and shapes (such as "stars" or auras associated with migraines) or images that appear to be complex theatrical stagings with people and animals. This broad definition makes them more common than one might think. These visions might have inspired the works of Lewis Carroll, Edgar Allan Poe, William Shakespeare, H.G. Wells and Charles Dickens.

Sacks keeps complicated medical terminology to a minimum, giving readers enough information to understand some causes of hallucinations without lapsing into medical lecture mode.

In the introduction, Sacks calls his book a "sort of natural history or anthology of hallucinations." He's particularly adept at giving readers an overarching view of hallucinations through time, finding just the right obscure journal article or bygone diary entry from which to quote.

But it's the first-person vignettes that breathe life into this book. Each chapter features personal stories of those who have experienced hallucinations. These tales are at turns delightful, entertaining, bizarre and sometimes downright terrifying. Those willing to open up to Sacks about their experiences did so in the hope of shedding light upon this misunderstood topic. They could not have turned to a more trusted source.

Rachael Hanel is a writer and university instructor in Madison Lake, Minn. She tweets at @rachael18.