Topographical Model of Mind
Freud finds that psychology should be divided into two levels from the analysis of dream: the unconscious mind and the conscious mind.
We may only feel our thought and memory in our conscious mind. We cannot feel the thought and memory in our unconscious mind, only under specific situation such as under psychotherapy, hypnotherapy or other ways, we may get the message in our unconscious mind.
Overly depress is one of the reasons led to mental illness. This is because the negative energy generated by the repressed emotions gets into our subconscious (unconscious) mind. Once the negative energy gets into our subconscious, we hardly notice it and it is difficult to fix it.
In our daily life, we always hear that some people lost control of their emotion and hurt their family members. This is because their subconscious mind is filled with negative energy that leads to psychologically breakdown.