Another update, 3 months later.
PDA is a type of autism where your body automatically goes into fight, flight or freeze when it perceives demands. This is because demands are incorrectly perceived as threats by the brain. This happens for all demands, even ordinary daily things like participating in a hobby I enjoy, self-care or a friend saying "let's hang out on Monday".
99% of the time I'm in freeze response due to PDA triggering all the time, but contrary to my previous-held belief, the freeze response =/= dissociation. When you are dissociated, you can still move your body around. Not moving isn't part of dissociation in and of itself.
When the body goes into freeze response for a long period of time, the word for it is tonic immobility. It occurs in humans who are subject to intense trauma, who couldn't escape with fight or flight. It seems like even though I am not going through intense trauma, my body incorrectly perceives so much threat that it causes this response. A more accurate term used to describe this is the flop response- it's where fight or flight to considered to be made up of 5 F's = fight, flight, freeze, fawn and flop. Freeze response describes tense and rigid immobility, which is not what I experience. During flop response, the body goes limp, which is more accurate for me. It's like the body is playing dead. Dissociation is also common, which is where I believe my initial misunderstanding stemmed from.
Both 'tonic immobility' and 'flop response' are descriptors, but are not the official medical term for this condition. The word for not being able to move for weeks or months is catatonia. It can co-occur with multiple different mental disorders. There is autistic catatonia as well, which I've found is most similar to my situation.
Considering this, I am in the process of waiting for appointments, but it's around Christmas now, so I'm going to have to wait quite a while.
In the meantime, I think I understand myself more now. Even something like the disability pension absolutely sends panic through me. You still need to complete obligations and requirements to have it, which I can't complete when I'm in a catatonic state, since I can't move. Also, those obligations being demands would trigger my fight or flight response, triggering the flop response- which is catatonia.
I believe the current system for receiving centrelink benefits significantly worsens my symptoms. I can't work and I can't receive benefits without going catatonic.