Australian Security Intelligence Organisation, ASIO.
When Nick Xenophon was a Senator, I asked a few questions. One reply was a little surprising.
"The first thing ASIO does when you are listed as a National Security risk, is to block access to your medical files."
This makes it impossible to get proper diagnosis and treatment.
If anyone you know has been "diagnosed with a mental illness" for thinking they are being pursued by government agents, try to access their medical files. You may only get an incomplete summary, not the actual files.