How can I stop a panic attack if I don't have my medication on me?

Ground yourself. Look around the room, or close your eyes if you would like, and just focus on where you are. Are you sitting in a chair, are you in your room, etc? Now focus on your feet. Feel the floor or ground you stand on beneath you and know that it is supporting you. Imagine roots growing from the bases of your feet down through the floor. You are safe. Repeat this whilst taking deep "square" breaths (Breathe in 4 seconds, hold 4 seconds, exhale 4 seconds, repeat). Nothing else matters but what you are doing right now, which is breathing. Let thoughts pass like rain. And when you feel clearer and calmer again, resume back to life one step at a time.

This is what works for me: Get somewhere you can just sit down and breath. I know your breathing will be speratic at first and you're ears are ringing and you probably feel like you're going to die, you won't. Just focus on your breath, trying to slow it bit by bit. It can also help if you count your breaths, getting to 10 then starting over again with each set trying to go slower and slower. Another thing I use is my braclet, I take it off and it gives me something to fidget with and focus on while I'm working on my breathing. You may consider carrying something like that with you, it can be anything, jewelry, a stone, hell even an old penny. Just anything you like. Anyways, I hope this helps you :)