If you are in the doctor's office and telling him that you want him to fax that to HR, then you are giving him consent. It's no longer a HIPAA violation. He is basically refusing your request to release a report of your health information to people that you need him to share it with. It is YOUR health information and his refusal to give it to you to give to HR is unethical.
Now, whether or not TDCJ should have a policy that requires you to share your medical information if you miss work is a whole other issue.