Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Insomnia is the most common sleep complaint, and manifests itself as feeling that one has not slept well or long enough. Most often it is characterized by difficulty falling asleep, awakening frequently during the night, or waking up early and being unable to get back to sleep. Most often however, insomnia is a symptom of a problem, and not the problem itself. Learn more about what is known about insomnia and the process of sleep, its effects on health in the following book.