I say "my injury triggered a rare disease in my entire nervous system". Im almost full body after 6 months and the thing people cant understand is how my hand could make my legs not work. People also pay attention to the word Disease, esp more than they do the words condition or syndrome. I think perhaps these two have become trivialised by how broadly they are used in modern medicine.
If I go any further, I will say it causes me also of pain and that I have a lot of similar neurological symptoms to MS! I do so thats not a lie, plus it explains my tremors and weakness. People know about MS so it gives them some direction on how seroius it is and what sort of disease it is. I also mention something like my NS is going crazy and is attacking its self, that sort of thing.
I just find a few key words help show how serious it is. and if you cn keep it limited to a few sentences it wont take so long to tell every one. I understand how you feel, who can be bothered, the story gets a bit old for us and most of the time they dont get it. I got mune from a burn injury, so if im not in the mood i cam just say nerve damage and leave it there.

Good Luck. also Im in South Australia, where abouts are you?