Sri Aurobindo
Letters of Sri Aurobindo
Volume III - Part 3
Your second experience is a first movement of the awakening of the inner being in sleep. Ordinarily when one sleeps a complex 
phenomenon happens. The waking consciousness is no longer there, for all has been withdrawn within into the inner realms of which we are not aware when we are awake, though they exist; for then all that is put behind a veil by the waking mind and nothing remains except the surface self and the outward world – much as the veil of the sunlight hides from us the vast worlds of the stars that are behind it. Sleep is a going inward in which the surface self and the outside world are put away from our sense and vision. But in ordinary sleep we do not become aware of the worlds within either; the being seems submerged in a deep subconscience. On the surface of this subconscience floats an obscure layer in which dreams take place, as it seems to us, but, more correctly it may be said, are recorded. When we go very deeply asleep, we have what appears to us as a dreamless slumber; but in fact dreams are going on, but they are either too deep down to reach the recording surface or are forgotten, all recollection of their having existed even is wiped out in the transition to the waking consciousness. Ordinary dreams are for the most part or seem to be incoherent, because they are either woven by the subconscient out of deep-lying impressions left in it by our past inner and outer life, woven in a fantastic way which does not easily yield any clue of meaning to the waking mind’s remembrance, or are fragmentary records, mostly distorted, of experiences which are going on behind the veil of sleep – very largely indeed these two elements get mixed up together. For in fact a large part of our consciousness in sleep does not get sunk into this subconscious state; it passes beyond the veil into other planes of being which are connected with our own inner planes, planes of supraphysical existence, worlds of a larger life, mind or psyche which are there behind and whose influences come to us without our knowledge. Occasionally we get a dream from these planes, something more than a dream,– a dream experience which is a record direct or symbolic of what happens to us or around us there. As the inner consciousness grows by sadhana, these dream experiences increase in number, clearness, coherence, accuracy and after some growth of experience and consciousness, we can, if we observe, come to understand them 
and their significance to our inner life. Even we can by training become so conscious as to follow our own passage, usually veiled to our awareness and memory, through many realms and the process of the return to the waking state. At a certain pitch of this inner wakefulness this kind of sleep, a sleep of experiences, can replace the ordinary subconscient slumber.
It is of course an inner being or consciousness or something of the inner self that grows aware in this way, not, as usually it is, behind the veil of sleep, but in the sleep itself. In the condition which you describe, it is just becoming aware of sleep and dream and observing them – but as yet nothing farther – unless there is something in the nature of your dreams that has escaped you. But it is sufficiently awake for the surface consciousness to remember this state, that is to say, to receive and keep the report of it even in the transition from the sleep to the waking state which usually abolishes by oblivion all but fragments of the record of sleep-happenings. You are right in feeling that the waking consciousness and this which is awake in sleep are not the same – they are different parts of the being.
When this growth of the inner sleep consciousness begins, there is often a pull to go inside and pursue the development even when there is no fatigue or need of sleep. Another cause aids this pull. It is usually the vital part of the inner being that first wakes in sleep and the first dream experiences (as opposed to ordinary dreams) are usually in the great mass experiences of the vital plane, a world of supraphysical life, full of variety and interest, with many provinces, luminous or obscure, beautiful or perilous, often extremely attractive, where we can get much knowledge too both of our concealed parts of nature and of things happening to us behind the veil and of others which are of concern for the development of our parts of nature. The vital being in us then may get very much attracted to this range of experience, may want to live more in it and less in the outer life. This would be the source of that wanting to get back to something interesting and enthralling which accompanies the desire to fall into sleep. But this must not be encouraged in waking hours, it should be kept for the hours set apart for sleep where it gets its natural field. Otherwise there may be an unbalancing, a tendency to live more and too much in the visions of the supraphysical realms and a decrease of the hold on outer realities. The knowledge, the enlargement of our consciousness of these fields of inner Nature is very desirable, but it must be kept in its own place and limits.