I don't think you should feel guilty or bad because you had an anxiety attack in front of someone else, how could that possibly be your fault, that is something beyond your control.
Do you ever feel guilty or bad after you have an anxiety attack? do you feel as if it was your fault? and felt bad for the person that you had it in front of?
I love the heartfelt answers you have already. I want to add Megan that most people who see your anxiety attack and know what it is... It's probably because they have them also or they know what you must be feeling or someone they love dearly has them. I think if you look at the world around you... (once out of high school and middle school) most people are kind. They don't "see" your attacks in the same light you do as your having them. They see someone who obviously has a major fear of something and are sympathetic. Please don't feel bad for being you.
You shouldn’t feel bad. You really have little control.