My favorite way with dealing with panic is to reflect on the Buddha, Dhamma, Sangha and put my mind on a confidence-inspiring object, and see how it tends to pass away. Other people have different ways of dealing with fear, but that is my favorite, it works for me. If we are going to die at any moment, there is no use trying to hang on to the body. We have to understand what we have refuge in and what we don't have refuge in. If we could die at any moment then we have to let go of the body. Fear and panic is normally concerned with trying to protect the body. So, for me I usually put my mind to the Buddha, Dhamma, Sangha to actually prepare myself to die.
It helps to note that the fear is there and have some practice in dealing with these mind-states. I have had some practice in dealing with this, in situations where I thought I was going to die. Fear did come up and then the mind said, "I haven't got time for this. I haven't got time to have fear." So the strength of the mind came up and just let the fear go because I didn't have time for it. But to get to that stage needs some practice in dealing with fear and what is important and what is not, and being able to reflect on death often so that you get in touch with your fears towards this body. When the fear comes up, if you are going to die at any moment, you really don't have time. So, there is no use waiting for that time, you have to practice beforehand watching fear and learning how to see the fear, see the agitation, see the thoughts come up.
For myself, when the thoughts came up and the fear came, I saw the attachment, "But what about Steve, what uhh... No I haven't got time for this. I am alone! I haven't got time for that." Putting the mind to, "If I am gonna die I want to be able to think of the Buddha, Dhamma, Sangha," which is my chosen object, and think of the Dhamma, and think of my potential and my strength, not my weaknesses at that moment. And it is amazing to see how powerful the mind gets at that moment. Reminding yourself of your strength and not your weaknesses, because fear comes from a sense of doubt in your ability to deal with these things. And so when the mind is stronger and resting in a joyful object then so what if the body is in pain. The mind can get joyful, but you have to have prior practice in reflecting in this way for such thoughts to arise.