A break in a person’s hold on reality (psychosis) can be caused by more than one mental illness. What you describe could be schizophrenia, schizo-affective disorder, a form of bipolar disorder, or more that I’m unfamiliar with. I forget what it’s called, but there’s an actual name for not believing in your own mental illness. It is worse than hell for the families around the person. I will look for resources. NAMI Family Support Groups are well regarded.