Strangely enough, this is not a book about schizophrenia--where the defining characteristic is to experience hallucinations. Instead, it is about hallucinations that occur in the context of drug use, sensory deprivation, torture, extreme fear, near-death experiences, dreams, and the like. Siegel has carved out a special niche in this area, having devoted his research, teaching (Psychiatry and Biobehavioral Sciences/UCLA), and clinical and forensic career as a neuropsychiatrist to studying the phenomenon and trying to fathom the relationship of it to what is happening in the brain. No passive observer, he is himself an experienced ""psychonaut."" Siegel presents 17 case studies, grouped under the headings of ""visionary drugs,"" ""dreams,"" ""imaginary companions,"" and ""life-threatening danger."" The cases are gripping--more so thanks to Siegel's graphic telling. Many are also horrifying: the story of two girls repeatedly raped after they had their drinks laced with ketamine, a drug that leaves subjects immobilized and hallucinating; the tale of a victim tortured by having deep skin flaps peeled away from his backside--and who somehow projected his agony into a scream that enabled him to detach himself from the pain. Other accounts include those of a sailor coked to the gills who conjured up a long-dead friend who guided him through a storm; the LSD flashbacks experienced by a pool hustler who was as good as the legendary Minnesota Fats; and Siegel's own experiences with peyote and shamans in Mexico, with a succubus-type of dream, and during a session in J.C. Lilly's water tank under ketamine. What makes the study especially meaningful is Siegel's no-nonsense attitude: Hallucinations really are all in your mind; many share common elements as the brain tries to make sense of circuits gone bizarre for one reason or another. Here the details are sketchy but fit the cases--which are unforgettable.