There is no obligations to disclose your private information to everyone. Especially medical information. It’s not even a lie. Just a common sense.

The only people who need to know you have hallucinations are your doctors. I think if you are getting married your spouse needs to know your basic health issues. Other than that I don’t see why friend needs to know.

Oh of course if you have something contagious, you need to inform people around you so they know to stay away or keep distance of other precautions.

Not telling everyone your private business isn’t a lie