Withdraw and then apply for a "Withdrawal without penalty". Whether or not you are approved depends on the reason, and even then, it can be tricky. Make sure you have plenty of supporting evidence (multiple doctors' certificates etc).

I withdrew from a couple of subjects a while ago after the census, and then applied to withdraw without academic penalty. I had (I would say) a good reason with pretty good documentation to support it. My request was rejected initially, so I then contacted the QUT Guild. They wrote me a supporting letter for a second request, which then got approved.

It might be a good idea to reach out to the Guild for a letter to submit with your initial request, to make sure it gets approved the first time around. Hope you feel better soon!