Being conscious or unconscious are subjective states known to all of us. Many have introspected about these subjective states: being conscious was associated with being awake--and being unconscious was associated with being asleep. Many thinkers developed general models or theories to explain these subjective states. During the late 19th and early 20th century, psychiatrists in medicine applied some of these insights into practical applications that appeared to improve mental health.
Beginning in the 19th century, experimental scientists began to go beyond simple introspection to discover what was going on in these states. To carry out truly scientific investigations, investigators could only study a small part of consciousness, and almost nothing of the unconscious. People in the medical field, and clinical psychologist felt that subjective reports about unconscious experiences--sometimes dream reports--were sufficient to improve mental health without any truly scientific support.
By now, the clinical approach has come under more scrutiny, and the scientific approach has broadened. But still, experimental scientific cognitive research only investigates a tiny sliver of what could be learned about consciousness--and an even tinier sliver of what might be learned about the unconscious.