Seems like it’s too late now to undo what you did. I think it would be illegal to get demoted or fired based on this information (it is a medical condition, after all). Your two options are to pretend like it’s no big deal or to have a discussion with your co-worker and ask that (s)he keep your confidentiality intact. (S)he may or may not, but you might feel better knowing you asked. The issue is that if you ask for confidentiality, your coworker might then think it’s a bigger deal than it is. I’m not sure what the best approach is.