Retainers. Depending on the correction to the teeth, many orthodontists fit you with a retainer you must wear in order for the teeth not to go back to their original position. Sometimes, mostly in the lower teeth, the retainer might be placed permanently.
Loose brackets. First, just take a deep breath and relax. You'll be fine. Second, call your orthodontist right away. You will need to find a time to go into the office and get them reglued to your teeth.