Ashtavakra Gita 12.7 -

Effects of truthful introspection are marvellous. None can set limits to spiritual reflectiveness. Mind and senses perceiving the gross elements like earth, water, air and fire, also perceive space surrounding them all, although space has no visible properties as the other elements have.

Likewise, the mind can pursue its thinking to any subtle level. That is how Janaka states that to think about the unthinkable Self is also to indulge in thought process. Discriminating thus, the seeker grows indifference to thinking itself and gets into unthinkingness. In fact, this is the way to lead all thought and modification process to stillness, and hence to their very source!

This is what happens in sleep every day. The waker withdraws from all sensory interactions as well as from all thinking, memorising, etc. To withdraw is not alone to disconnect from senses and mind, but also to dissolve into what is deeper within, the very source of all outer and inner processes!

In sleep one is immersed in that source, but not being aware of it. Nature induces sleep. It is a biological phenomenon.

In spirituality, the seeker has to get to the source, but consciously. He has to accomplish it while being wakeful. Knowledge, knowingness and its pursuit alone will take to this final goal. That is why Janaka deliberates so subtly and wholesomely like this.