Using sick leave from school but working in another industry.

Posting under a burner account for obvious reasons.

Recently I have taken a job outside of the industry, I was in a position that the school allowed me to take a period of time off as leave without pay.

I wont go into details, however the past two years haven't been pretty, my general and mental health declined significantly. I am content in the job, albiet with a pay cut, and do not wish to return to teaching.

I have a huge amount of sick leave that will disappear if I pull the pin at the end of my LWOP.

I know ethically and morally this isn't right, however I am considering speaking to my GP about the extreme anxiety of potentially returning to the classroom and using at least some of the sick leave whilst continuing to work in my current job.

Is it possible (and legal) to be on long term sick leave from teaching and picking up work in another industry?

NSW non government for context.