My sister disclosed my previous condition of pseudoseizures, (from anxiety) caused by meningitis.This was 10 years ago.She disclosed it to the nursing

Defamation is the publication of a false defamatory statement of fact about a person.  From your question, it sounds like the information your sister disclosed was truthful, not false.  Moreover, the statute of limitations for defamation is one year.  Since the disclosure occurred ten years ago, any claim would probably be barred by limitations.  With the exception of nominal damages for certain types of statements which are considered defamatory per se, your question does not indicate how the disclosure caused you to suffer any sort of compensable damages.  Finally, disclosing past medical history to nursing staff probably isn't defamatory.