I have read that the health thing has to do with how much strain the person will put on the health system, which I believe the general number I've seen on this forum is $40k over 5 years though I've read $21k over 5 years in other forums as well.
They don't expect applicants to be in perfect health, so don't stress too much. If you're truly concerned, speak to a registered migration agent that specialises in health issues and medicals for visa applicants. I believe at least two frequent this forum but someone else will have to tell you which agents they are.
Best of luck.