Sleep disturbances including insomnia are associated with and can comprise core features of anxiety disorders. Intense fear and behavioral avoidance of certain things or situations are hallmark features of phobic disorders. Obsessive-compulsive disorder (OCD) features recurring intrusive thoughts that seem irrational to the individual, and behavioral rituals that are excessive and related to obsessive thoughts. The core feature of generalized anxiety disorder (GAD) is persistent, uncontrollable worry. A unique pattern of distressing somatic symptoms also differentiates GAD from other anxiety disorders in adults as well as children. The core feature of panic disorder (PD) is recurrent and unexpected periods of extreme fear that occur in a sudden, crescendo-like manner. Anxiety related to separating from parents or caretakers is a normal aspect of child development that for children subsides by age 3. Post-traumatic stress disorder is an anxiety disorder that develops in children and adults exposed to threatening events.