Forget the CAD if you aren't well don't fly it's as simple as that. It's your responsibility, not to break the law. They are trying intimidation tactics, so what call them on it! Speak to the duty manager and explain that you are not well but if he orders you to go flying, ask him to put the order in writing and include that he is acknowledging your health state but considers you fit for duty. Trust me you will never receive that letter. Go and see the Cathay Doctors if you are unwell or your own GP get a certificate to CYA but do not go to work sick. You are putting the lives of all the people sitting behind you on the line. It is not fair to them