In the night dream, you lose self-awareness and self-ignorance alone remains. Here, you are overcome by your self-ignorance induced by sleep. In this sleep-dream, you are not creator, controller and destroyer of any item of the dream. This dream is also a world of imaginations only and is as good as an imaginary daydream you have in the awakened state.
The creator, controller and destroyer of the sleep-dream is the bundle of thoughts stored in your memory (chittam).
This memory at the surface level is full of thoughts of this birth only. The deep level of this memory (called as sub-conscious state) is full of very strong thoughts retained by the memory during past several births. This sub-conscious state contains very few thoughts only, but those thoughts are as strong as diamonds. This sub-conscious state decides the real behaviour of the soul. The memory in the surface level contains many thoughts, but, no thought is strong.
The state of consciousness (surface level) may receive a point from a divine spiritual preacher. If the opposite point is in the sub-conscious state, the practice will be as per the sub-conscious state only. These strong diamonds in the sub-conscious state are called as samskaras or vaasanas. If the samskara is congenial to the preaching received, the preaching is immediately implemented in the practice. If samskara is opposite and still if you want to implement the preaching received, you have to strengthen the preaching by constant memory so that your samskara gets defeated by the preaching present in your surface-conscious level.
Receiving the concept from the preacher is called as ‘Shravana’ (hearing), continuous memory of the concept is called as ‘Manana’ (constant recollection) and the concept becoming samskara by accumulation of strength is called as ‘Nididhyaasa’ (solidification of the concept as firm decision). The Veda says about these three stages one after the other (shrotavyo, mantavyo, nididhyaasitavyah).