In insomnia, which is a very common sleep disorder, objective sleep measures, EEG activity, physiologic findings, HPA axis activity, and inflammation markers suggest that it is not a state of sleep loss, but a disorder of hyperarousal present both during the night and the daytime. Several psychological and physiological factors contribute to the onset and perpetuation of insomnia, such as anxious-ruminative personality traits, stressful events, age-related sleep homeostasis weakening mechanisms, menopause, and biologic-genetic diathesis of CNS hyperarousal. The therapeutic approach in insomnia should be multidimensional, reducing the overall emotional and physiologic hyperarousal and its underlying factors present throughout the 24-hour sleep/wake period.