I don't know the laws in AU, but i have only been commented for serious self-harm that was life-threatening. The other commitments were for major depression and they said i was suicidal. I know in treatment for self injury, it is generally not done (involuntary commitment for it) and considered not so helpful. As stated by sam and others, it breeds resentment. Here, doctor and treaters with little experience with self harm are the ones to hospitalize for non-lethal self-injury. Can you talk to your therapist and gp and come up with a safety plan? Would your gp work with you to find alternatiVes to hospitalization? Generally, hospitals in the US are only good for containment and meds (no therapy). It sounds like you may needed to get to the root of why you are self-harming more now and work on that.
Good luck (sorry for errors, my phone is not good on forums)