The 772 that OS (Austrian Airlines) uses is a great plane for those that feel cramped. The overhead is open making people feel less confined.

Stay hydrated and take walks around the plane if you start feeling anxious. Maybe bring a "calming" tea with you and just ask for hot water. You're far from the only person to have issues with flying. Once you get to Chicago if you're having problems you can always go by rail. It's a long ride but it's an option.

Welcome to America.