boss and manager digging to find my medical diagnosis

my boss and manager are pissed that I haven't disclosed my medical condition to them (I have taken some sick days). they keep begging my coworkers to tell them. based on some solid info, I know that if they found out my diagnosis was a serious mental illness, they'd fire me. I know this is illegal, but then what? I don't want anything to do with the legal system. I hate this bullshit