Where in Australia are you?
I'm in Brisbane. I've just suffered another concussion after having PCS for the last year. It's funny but I feel the depersonalisation you describe more with this latest concussion then the last. But I am hopeful because I got over it before so feel like I can again.
Find a good physio. A bit tough I know because there are so many of them but shop around a bit. If you don't have private health cover think about getting it. I was treated publicly for quite a while but didn't really improve until I started seeing a private physio. It was a bit tough financially but worth it.
Have you tried a psychologist? Another known symptom of PCS is depression and anxiety. I was referred to a neuropsychologist who specialises in people with chronic pain. I'm an engineer also so was sceptical at first, but it did help, especially when she explained that certain regions of the brain can become 'dormant' so to speak when we are in chronic pain such as those controlling emotions or those giving us our sense of being present.
Good luck.