Good general information about several specific kinds of anxiety problems is available at National Institute of Mental Health . A part of this site The Causes of Anxiety and Panic Attacks is an article written to help patients understand the physical and mental aspects of anxiety and panic reactions. When there, find the menu and click on anxiety or stress. Focusing on Panic Disorder , is a medical-oriented site which explains the development of panic and its treatment using medications. Offering a slightly different approach, Treatment for Panic is based on Cognitive-Behavioral Therapy methods and suggests medication, as needed.
Drugs are important in some cases.
And, in my opinion, if cognitive techniques, exposure, and drugs don't work, insight therapy probing the childhood history should be tried.