When a psychologist makes a decision that will promote honesty within the field of psychology, which ethical principle is that psychologist practicing?

A general principal: integrity.

In this activity, psychologists are honest, fair, and respectful of others. In describing or reporting their qualifications, services, products, fees, research, or teaching, they don’t make false statements. Psychologists strive to be aware of their own belief systems and the effect of these on their work.

They probably don't understand either 1. what the nightmare is about or 2. his anxiety and stress