Filing a case of defamation at work leading to termination

My Facebook profile about my depression state was shared with people at work who showed to me and also confirmed in writing addressing the issue via email confirming my post was shared with them.

This has caused a lot of damage to my reputation in the workplace and which led to my termination under the false pretence of underperformance during the probation period.

They also had facts and records to prove that my performance was good but due to my reputation at work, I was wrongfully terminated.

I want to know from a legal point if I want to press charges on the people who showed and circulated my Facebook post which was non-work related, how can I exercise my rights as an abiding citizen?

Thanks.