Mine was caused by a drug phase I went through a few years ago.
I was assessed and told "you're almost there, but not quite" and diagnosed me with schizoaffective disorder but after reading up I'm not sure that's accurate.
It seems lm closer to "paranoid personality disorder" but Ugh.. It's all labels anyway. 
I was wrongly diagnosed with a sort of Psychosis problem when I was a teen (14), I didn't know until i had been on a medication that has been known to cause brain damage/brain problems if stayed on for more then a year. I took it for 7 years. After that I was more properly diagnosed with Aspergers and quite assertively told to stop taking that first medication by 5 different Gp's and a psychiatrist, all after I graduated highschool of course.
So Donk may know, the Aust. Government (well Abbott) changed their Disability Support Pension requirements to meet? I still qualify
been on it since I was 19. Had an assessment, medical review and interview last month to see if I can work without causing me (or others) more harm mentally/emotionally etc *mutters*.