I have so far considered the relationship of sleep and suggestion. I have now to deal with the relation of sleep to other processes of the unconscious. Sleep affords a striking example of suppression. Not only does the conscious activity of the waking life disappear, but any experience acquired in sleep is forgotten, or tends to be forgotten, when we awake. The sleeping experience which is suppressed may be of the kind I have already mentioned in which a person may be wholly unaware of what he had said or done in sleep.
Dreams provide an equally characteristic example of forgetting.
One of their most definite features is the ease with which they are forgotten. It often happens that we only become aware that we have dreamed owing to some event of the day which recalls an image or incident of a dream which has occurred during the preceding night, or even on some more remote occasion. This has often raised the question whether sleep is not habitually accompanied by dreams, only a small proportion of which are remembered. Whether this be so or not, we can be confident that dream-experience bulks largely in the content of the unconscious. We all know that dreams differ greatly in the ease and completeness with which they are forgotten.