The big rule on this is that you should not out-and-out lie about your condition, but that doesn't mean you need to explain things. Like I've taken days off and

The big rule on this is that you should not out-and-out lie about your condition, but that doesn't mean you need to explain things. Like I've taken days off and explained to my boss that I have a personal medical condition that needs taking care of. This is usually fine for an occasional absence or down day. For complex situations where your boss may want to know what's going on so that he can plan critical activities, there's not a simple answer.