Hi.
The thought of going back to school is enough to make a lot of people break out in a cold sweat; the fun-and-games high school of TV and the movies sometimes strays far from reality. Sometimes it feels like everybody is plotting against you or just being mean for the fun of it. However, while school can be traumatizing, it doesn't have to be a terrifying experience.
What seems to be bothering you most is the thought of returning to your judgmental classmates. Well, one thing I would suggest is that you come into the situation without judgments of your own. Maybe with a fresh attitude, you'll discover that many of your classmates have the same fears about returning to school that you have.
Of course, I don't know your history with these people, and perhaps they really ARE all judgmental and jerky. If this is the case, you may want to try a few other things to help you get through high school unscathed. You might try to focus more on your interests or talents, or on the point of school itself: to help you learn and be prepared for the future. Try to find things during the school year that will really make you happy and also give you room to relax and feel good. It sounds selfish, but so what? Focusing on yourself and your happiness is essential in any environment that feels hostile.
If you begin to find that your panic attacks are becoming more frequent or more serious, you may also want to talk to someone about your fears. In any case, it's important to look at the big picture: High school really is a temporary situation, even though it might not seem like it right now. Good luck, and take some deep breaths.