Working place illness

Hello! I currently work as a full time retail associate in NSW. My job has implemented a new system that requires us to fill out a survey when we return from sick leave. This asks for the exact reasons for illness, as well as any prescribed medication and how long you will be using it, listed side effects, whether the condition effecting you is chronic or temporary. Obviously a doctors certificate in these situations is required, but do I have to tell them the exact nature of my illness? I really don't feel like a retail manager needs to know what medication I use.