A huge factor in panic anxiety disorder is ideal hydration with the correct balance of electrolytes/sodium balance. Many people seem to lean towards overhydration which dilutes the sodium levels in the body, creating a panic anxiety response. It's a tough situation. It seems to be an area of "cycles"... Anxiety breeds Anxiety, and before you know it, you're stuck in a vicious cycle that's hard to get out.
I find that if I pace myself drinking water(without pounding liter after liter in a short amount of time), I feel very calm like all functions of my body are in perfect harmony. When I used to be more addicted to water, or having the common fear of, "I'm not drinking enough, I'm getting dehydrated, etc..", I could feel the anxiousness kicking in.