You have the right to make choices about your medical treatment and put legal agreements into place to ensure that your wishes are followed.
In Australia, the law recognises a person's right to control their own lives. People are presumed to have the capacity to make decisions for themselves unless proven otherwise.
'Capacity' is a person's ability to:
understand the nature and effect of decisions
freely and voluntarily make decisions
communicate those decisions in some way.
'Impaired capacity' is when a person can't do these things.
Impaired decision-making capacity may be due to an intellectual disability, acquired brain injury, mental illness, dementia or some other cause.
An appropriately qualified health professional can determine impaired capacity.