Q: While waking I know myself as awareness. But, if I am awareness which is permanent (Sat), why don’t I know myself during deep sleep?

A: It is your intellect that knows that you are not just body-mind but are awareness. It is your intellect that has got enlightened. You are pure awareness who is just powering the act of knowing by the intellect just like electricity powers a gadget. Since intellect is not operational during deep sleep, the sense of knowing is not there.

During the waking state, there is apparent subject and object split. So, it appears that your intellect (subject) is perceiving something (object). During deep sleep there is effectively no subject/object split and hence there is no perception*. This subject/object split during waking state is due to the apparent world. There is no world in deep sleep state and hence there is no subject/object split.

Awareness is silent witness. Whether something is known by the intellect or not awareness is witnessing that. In waking/dreaming, awareness is witness to the perception and in the deep sleep, awareness is a witness to the lack of perception.

*Strictly speaking, even during deep sleep there is residual/dormant subject/object split. A familiar experience of this can be of disturbance in sleep due to loud noise/mosquito bite.