Mental illness is obviously a hugely debatable topic.
As a Mental Health Student Nurse, I may be slightly biased. But seeing people with actual mental illnesses really does open your eyes to it.
However, people can have mental illnesses, but they do not necessarily have to be unwell with it.
They could be managing fine, and remain well for short/long periods of time, if not forever.
Just because they are well at the moment, does not mean the mental illness does not exist.