We have somewhat diverged, however, from our main theme, to which we must now return. We have seen that the subconscious mind may become, so to speak, _diseased_--this consisting very largely in the processes of dissociation, complex formation, etc. Further, we have seen that this dissociated, automatically-acting "self" may exist either as a separate stream of thought running alongside of, or rather _below_ the main current; or may alternate with it, by rising to the surface and occupying the whole stage to the exclusion of the normal consciousness--when we have those cases of alternating or multiplex personality which have so puzzled psychologists for many years--and the correct interpretation of which we are only just beginning to realize. When this complete change of "self" has taken place, we have those cases of altered personality referred to at the beginning of this chapter--cases which are tragic in the extreme in many instances, but which represent merely extreme types of those losses of memory from which we all suffer, to a greater or lesser extent, even in our normal life. The restoration of lost memories by means of suggestion--the synthesis of the dissociated states--_this_ is the key to the mystery, the great secret of modern psychotherapy. And this theory of dissociation of consciousness has enabled us to explain many puzzling facts hitherto inexplicable. Thus _hysteria_, with its multiform symptoms and its internal contradictions, has long been the stumbling-block of medicine. Now it is no longer thought to be a morbid state (dependent usually upon sexual disturbances), but it is regarded rather as an indication of the splitting of the mind, a dissociation which embraces all the motor, physical, and psychical activities. On this theory, hysteria is easily explained and all its multiplex symptoms understood. In treating it, the self is unified, abnormal suggestibility is removed, and the patient is cured! _Psychaesthenia_ again, with its obsessions and fears, may be explained in the same manner, and its cure rests upon the same principles. The "attacks" cease so soon as the psychical synthesis is effected and the morbid self-consciousness removed. _Neurasthenia_, long regarded as a pathological state, due to auto-intoxication and similar causes, is now thought to be due chiefly to dissociation, caused by excessive fatigue--one of the known contributory causes to this condition. _Psycho-epilepsy_--a sort of fictitious imitation of the real disease--is due to precisely similar causes, and may be cured in a similar manner.