How can others act when I am having a panic attack?

They need to be calm and cool so they can think rationally about helping you or just being there for you. If they are also set into a frantic state then this would add fuel to your attack. If you want you could talk to them about what helps you calm down so they know just in case. They should be practical and tell you to take deep breaths or go outside for a minute, they shouldn't make a face or look out of place as this will make you feel even worse about having one. They just need to act like they are trying to get you through it.