It is the truth that mentally unhealthy people never doubt of the ps...

[Anja]

It is the truth that mentally unhealthy people never doubt in mental health?

[The anonym]

Lie.

[Efremov A.G.]

Mentally sick it is enough often understand, that with them not that's all right. An another matter, that under influence of illness or disease, by virtue of its or her intensity or duration, they can lose criticality in relation to themselves and to the actions. Here then they can deny at themselves disease.

[From my experience]

The sick person, as a rule, is convinced of own correctness (at maniakalno-a depressive psychosis), for example. And for it or him all around of "patients", but only not he.
And with other diseases can be differently, certainly.