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.