There are several considerations, for example
1) is chemistry your worst subject?
2)Do you like chemistry(forget for a moment it is content heavy, focus on the content you learn, do you enjoy it?)
3)Have you done your first assessment for chemistry, and if so, how do you feel about your marks
4) Are you willing to put in the time to study chemistry?
The above are just some of the questions you should consider when dropping a subject at the start of your HSC year, only drop it if your answer to the above questions indicates you are not interested in chemistry and probably will be unable to allocate enough time for it, it is arguable that physics is also a very content heavy subject-in many aspects, it is more theoretical than chemistry, I truly admired you for the fact you are able to overcome/overcoming your health issues and studying hard, remember, you have got 6 weeks of summer holidays to catch up, so it is not impossible, if you have any concepts you don't understand or are behind on, why don't you ask your teachers for help(teacher love students asking questions), ask them on bored of studies forum, and for some of your subjects, like advanced and extension one English(only for ATB), and chemistry and physics, if you have any questions you don't understand now, any concepts you are behind on, you are welcome to pm me anytime
Just make sure you think through and ask for advice before you drop a subject-because once you drop it, you can't pick it back up again-all the best of luck for this year, make sure to rest wherever you feel you are getting too stressed
hope this helped