Hannah,
I was lucky that my friends were supportive when I began having anxiety attacks... esp. since I when from being the carefree, fun-loving, "life of the party", to becoming extremely fearful, confused, and quite withdrawn. I did, however, notice that some of these friends, with time, became frustrated when I changed plans, or would make passive-aggressive comments about me not going out as much. I understand where this comes from, but it still happens sometimes, and it still hurts.
The thing about panic is that while we cannot understand our friends' and colleagues' reactions, they also cannot understand what we are going through. That's why support groups exist, and are so important. The other thing about panic and anxiety is that it can, at times, make us somewhat self-absorbed... we are overly concerned about our every symptom, and we can frankly become less fun to be around, and even less supportive as friends. It is important to understand what role WE are playing when people start treating us differently.
I hope the last bit I wrote does not make you feel worse, but help you examine what you can do to help make things better for yourself. In the meantime, the support group is an invaluable resource, where we are all experiencing the same things and can understand each other like no one else!
I hope you can maintain the friendships that are really worth maintaining, and I hope we all overcome the anxiety and panic together!