Borderline states

Borderline states of psychological integration exist where a person has not yet broken with reality, but where they may develop psychosis when under stress. This is therefore a term used in a clinical context, usually related to the idea of personality disorder, particularly [borderline personality disorder.

Psychoanalytic view
In psychoanalysis borderline states would be seen as arising due to the breakdown or inffectiveness of an individuals defence mechanisms and difficulties in maintaining reality testing