I was on medical leave. I was asked to provide documentation to return to work. I provided that documents and was still terminated.

I do not see a question, but the request that you provide return to work documentation is not, by itself a violation of the law.  It also is not a violation of the law that you were terminated due after you provided the documentation.  However, there could be a violation of the law depending on the reason for the termination.  You should consult with an experienced employment attorney to discuss further. Employers are not covered by HIPAA.  The entitites that are covered by HIPAA are: health care providers, health plans, health care clearinghouses.  Even if your employer might be one of these entities, it would not give you a legal claim related to your employment.  You can find more information on this on the website of the U.S. Department of Heath and Human Services (hhs.gov)