The Interpretation of Dreams by Sigmund Freud Chapter 1 Page 7

sensations of haunting dread remain as strange to normal consciousness as do dreams to our waking consciousness; their origin is as unknown to consciousness as is that of dreams.

It was practical ends that impelled us, in these diseases, to fathom their origin and formation. Experience had shown us that a cure and a consequent mastery of the obsessing ideas did result when once those thoughts, the connecting links between the morbid ideas and the rest of the psychical content, were revealed which were heretofore veiled from consciousness. The procedure I employed for the interpretation of dreams thus arose from psychotherapy.

This procedure is readily described, although its practice demands instruction and experience. Suppose the patient is suffering from intense morbid dread.