Everyone worries and has fears in appropriate situations. In some circumstances, fear can be lifesaving, and the body's response to fear is called the fight-or-flight reaction. When anxiety (worry, fear, apprehension, or unease) happens over otherwise common things or events, is difficult for the individual to control, is excessive, and lasts at least 6 months, this is called generalized anxiety disorder. Along with the other types of anxiety disorders (obsessive-compulsive disorder, panic disorder, social anxiety disorder, posttraumatic stress disorder, and phobias), generalized anxiety disorder is fairly common. Unlike the separate episodes of severe panic anxiety that occur in panic disorder, the level of anxiety fluctuates gradually in persons who have generalized anxiety disorder. Anxiety disorders affect more than 40 million adults in the United States alone, about 18% of the population. Worldwide, approximately 20% of persons who receive primary health care have anxiety disorders or depression.