Is anxiety problems a valid reason for missing school for two weeks..?
This is definately a valid reason for missing school. Unfortunately your teacher may be one of the many people who don’t understand it without the explanation coming from someone like a doctor. Go and speak to your doctor who will give you a note for school, help you to understand what is happening in terms of your anxiety and possibly refer you to a psychologist who will be able to help you overcome the panic attacks so you can get back on track.