Sri Aurobindo
Letters of Sri Aurobindo
Volume IV - Part 3
The difficulty of keeping the consciousness at night happens to 
most – it is because the night is the time of sleep and relaxation and the subconscient comes up. The true consciousness comes at first in the waking state or in meditation, it takes possession of the mental, the vital, the conscious physical, but the subconscious vital and physical remain obscure and this obscurity comes up when there is sleep or an inert relaxation. When the subconscient is enlightened and penetrated by the true consciousness, this disparity disappears. The Pishachic woman that tried to enter [in a dream] is the false vital impure Shakti – and the voice that spoke was that of his psychic being. If he keeps his psychic being awake and in front, it will always protect him against these dark forces as it did this time.