What is anxiety? Symptoms Types Causes Treatment Prevention Takeaway Anxiety is a normal and often healthy emotion. However, when a person regularly feels disproportionate levels of anxiety, it might become a medical disorder. Anxiety disorders form a category of mental health diagnoses that lead to excessive nervousness, fear, apprehension, and worry These disorders alter how a person processes emotions and behave, also causing physical symptoms. Mild anxiety might be vague and unsettling, while severe anxiety may seriously affect day-to-day living. Anxiety disorders affect 40 million people in the United States. It is the most common group of mental illnesses in the country. However, only 36.9 percent of people with an anxiety disorder receive treatment.