Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The term “hallucination” refers to a perception in the absence of any external stimulus while the affected person is conscious and awake. Common types of hallucinations include tactile, visual and auditory hallucinations. Although there are forms of hallucinations related to smell or taste, they are rare. Learn more about the phenomenon and its main forms as well as its causes and treatment in this book.