Try and get out in the fresh air as soon as possible, and if you're at work try and have a desk fan nearby so that you can aim it at your face. A really cold drink of water works wonders and Body Shop do a heavenly smelling relaxing aromatherapy spray that you can aim at your face/head. (Take your glasses off first if you wear them!) It's never as obvious to other people as it is to you if that's any comfort.