The waking consciousness takes notice of only a very small fraction of all of the impressions that reach the senses. Not all impressions are direct sense impressions, as some impinge directly on the aura or on the mental substance without involving the 5 external senses. Of those directly noted, only a small percentage are actually accepted consciously and acted upon. While we do not generally take cognizance of them, these impressions are captured and held in the subconscient being. When the waking consciousness withdraws, and along with it the active mental control that it exerts, the unnoticed and ‘undigested’ impressions have the ability to rise and take the form of dreams in many cases, as well as a general restlessness during sleep.
When we live an isolated life, away from modern media and the energetic force of modern society, we obviously do not capture as many of these impressions directly as we do if we are actively involved in the external life of the world. For example, as the world has become hyper-sexualized in its imagery and energy, even those who are focused on other things, or who actively reject sexual energies from their being are exposed to the impressions that get embedded in the subconscient layers of the being, there to arise when the control is absent, or when somehow triggered by some past experience, event or formation.
The spiritual seeker may avoid sexual expression or focus and yet have an experience in dream. This can be seen as a highly positive fact, as it implies that the sexual tendency has been mostly reduced or eliminated from the active consciousness. The risk, and therefore, the area for required vigilance, is that when the sexual dream arises the seeker will accept it or even, allow it to gain a foothold in the waking consciousness through action, or through imagination or visualization.
The sexual impulse, as it is so deeply bound to the physical and vital nature, will always attempt to reestablish itself through environmental pressure, through the rising of sexual impulses in the subconscient, and from there, an attempt to obtain the acquiescence and active support of the waking consciousness.
At a certain point in the sadhana, it is possible for the seeker to become conscious even in sleep, to maintain his dedicated aspiration and thereby to reject the pressure if it tries to arise in dreams. Note that becoming conscious in sleep does not mean fighting to stay awake, but rather, to infuse the aspiration so completely into the consciousness that it permeates even the subconscious realm of the being.
Sri Aurobindo observes: “This kind of sexual attack through sleep does not depend very much on food or anything else that is outward. It is a mechanical habit in the subconscient; when the sexual impulse is rejected or barred out in the waking thoughts and feelings, it comes in this form in sleep, for then there is only the subconscient at work and there is no conscious control. It is a sign of sexual desire suppressed in the waking mind and vital, but not eliminated in the stuff of the physical nature.”
“To eliminate it one must first be careful to harbour no sexual imagination or feeling in the waking state, next, to put a strong will on the body and especially on the sexual centre that there should be nothing of the kind in sleep. This may not succeed at once, but if persevered in for a long time, it usually has a result; the subconscient begins to obey.”
Sri Aurobindo, Bases of Yoga, Chapter 4, Desire — Food — Sex, pg. 80
Sri Aurobindo Studies 