Anxiety is a feeling of extreme nervousness, worry, or apprehension. There are several types of anxiety disorders, including generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), and panic disorder. People with anxiety or an anxiety disorder tend to worry about things that are not generally a cause for concern, and may feel that they are in danger or experience panic. Anxiety and anxiety disorders can cause physical symptoms, including fatigue and weakness, trembling, heavy breathing, rapid heart rate, and sweating. Anxiety disorder symptoms can range from mild to severe, with severe anxiety impacting the ability to function in daily life.