Breathe into a small paper bag, remember to breathe in the contents of the bag. When you start hyperventilating during a panic attack your body loses carbon dioxide, thats why you get numb in certain parts of your body. The paper bag helps replenish the c02 and will make you feel better.
See a doctor or psychiatrist, panic disorder is easy to treat but not always so easy to get under control. Personally, i find benzos (xanax, klonopin, valium, etc) to work great and i have horrible panic attacks that land me in the emergency room.