When you are hit by an anxiety attack in public, do not try to escape but if you have the possibility, make a few steps. Your knees will not collapse. Your breathing might be a bit quicker than usual but nobody will notice it. Then look around in the room. If you are outside, your vision can be broader. In any case, looking around is helpful . Your eyes get a movement that can help calm down your brain. You can move your eyes looking forward, then looking to the ground and then to the ceiling without moving the head. Nobody will notice it. But your brain gets stimulated in the sense that both hemispheres start working together. Do this movement just a couple of times.
If you cannot leave your chair, try to move your toes inside the shoes. This movement takes your attention and the movement itself helps your blood circulate better. Then press, with the nail of your thumb, the inner edge of the nail of your little finger. It hurts but it is good for your overall well-being and nobody will notice this little movement. Then, with the nail of your thumb , rub three times every finger cup until it hurts a little bit. Do this movement of three times rubbing the finger cups three times in a row. Nobody will notice your movements.
You, instead, will immediately feel better!