I think what's helped me the most in dealing with anxiety is learning about what is actually happening inside of my body when the impending doom starts to rear it's ugly face. Back when I had no idea what was going on with me the attacks would be 100x worse.

So, the physiological symptoms of anxiety (pounding heart, nausea, muscle tension, shaking, etc.) are similar to the symptoms of an actual response to danger. Because we use somatic sensations to inform our comprehensive experience of the world, these physiological and psychological symptoms play into each other in a way that can quickly spiral out of control into a full-blown panic attack..

Usually, the initial attack would start with a physiological sensation - say nausea, or clammy hands - that may be due to any number of factors (like blood sugar being too low). But, the body subconsciously interprets those symptoms as being rational responses to a real threat that haven't yet consciously been identified. Once this connection is made, you pay more attention to the physical symptoms like a heaviness in your chest, or a churning pit in your stomach, and become more anxious - your body then releases more and more adrenaline and cortisol - which, of course, leads to even greater physical symptoms to become even more anxious about. You then begin to catastrophize the situation with racing thoughts and become blind to the fact that there is no real danger. As you try to consciously identify the threat, you'd be far enough into the process that you would attribute the anxiety to the growing possibility that you're going to pass the hell out, have a mental break, throw up, or even die.

It's simple: You're panicking because you're panicking.

Knowing this hasn't necessarily cured me from it from happening, but nowadays I can usually catch one early enough to stop it in its tracks before the "holy fuck I'm dying call the ambulance!" stage.