Relax. Assuming that you don't have a medical condition that needs to be treated by a doctor, the simple answer is to relax. Many people find yoga and other relaxation techniques to be helpful. Others find peace through prayer and meditation. For most of you i would encourage you to visit with your physician to find out the cause and then get proper treatment in order to get well.
Look for cause. This is a major problem with a great number of people and causes a great deal of distress and misery. It is always best to determine the cause of the anxiety and panic, and there are many causes. Most often humans need professional help to find the causes and then proper treatment can give relief and hope for a more normal life. Call your physician for help.