Deep mental activity generates heat, which keeps off deep sleep. Cold in its intensity wakes you up. Deep sleep brings on a sense of happiness and peace with it. This experience we get only in the absence of all mental activity. When we direct our mind to this happiness aspect of deep sleep, we feel a sensation of gentle coolness, which wards off all sense of negation in sleep.
So we get to our real nature by relaxing our mind from all forms of activity, and at the same time not losing sight of the happiness and peace experienced in deep sleep.
This positive aspect saves us from the probable shroud of negation and slumber. We should not allow the mind to be active and at the same time we should see that it does not become inactive.
In other words: Sleep knowingly. Thus, deep sleep can be utilized directly for establishing oneself in the real center.
Atmananda Krishna Menon