It has become accepted dogma in the scientific community that studies the phenomenon of dreaming that there are various stages of sleep, and that dreams only occur in what is called “rem sleep”, but that there are “deeper” levels of sleep, known as dreamless sleep, in which no dreaming occurs.
Sri Aurobindo however takes another approach to this question: “But, in fact, in what we call dreamless sleep, we have gone into a profounder and denser layer of the subsconscient, a state too involved, too immersed or too obscure, dull and heavy to bring to the surface its structures, and we are dreaming there but unable to grasp or retain in the recording layer of subconscience these more obscure dream-figures. Or else, it may be, the part of our mind which still remains active in the sleep of the body has entered into the inner domains of our being, the subliminal mental, the subliminal vital, the subtle-physical, and is there lost to all active connection with the surface parts of us.”
The question is thus, not that dreaming suddenly ceases when we go into a deeper state of sleep, but that we are simply unable, under normal circumstances, to bring awareness to this state of consciousness and thus, we are unable to access the dreams that occur at this level. Sri Aurobindo continues “But if we have gone deeper inward, the record fails or cannot be recovered and we have the illusion of dreamlessness; but the activity of the inner dream consciousness continues behind the veil of the now mute and inactive subconscient surface.”
There are states of awareness that can be developed wherein we can actually participate in, and gain awareness of the dream consciousness of these subliminal states, and in fact, the subliminal planes open up vast new opportunities for experiences beyond those of the individual. Carl Jung spent the greater part of his career working to gain understanding and access to the subliminal realms which he called the “collective unconscious”. These realms provide archetypal images which represent deeper forces and motive springs of action than the individual can draw upon from his own limited experiential life.
reference: Sri Aurobindo, The Life Divine, Book 2, Part I, Chapter 5, The Cosmic Illusion; Mind, Dream and Hallucination, pp. 423-424