Health is a spectrum. Perfect health and being free from illness/sickness are different states. At least according to this guy and some other people.

I would argue perfect health doesn't exist, but there's a certain point people can reach where they are perceived as healthy by others. Especially when it comes to mental health. Really comes down to the question of what "health" means and if treatment is necessary.

edit: my personal definition of unhealth is the inability of an organism to regulate itself.