Sri Aurobindo
Letters of Sri Aurobindo
Volume I - Part 1
Fragment ID: 9820
It [sleepiness] is the physical tamas trying to push itself into the place of the calm. Part of the transformation consists in replacing the element of tamas in the nature by the śama or true calm, peace, rest, of which tamas or inertia is the degradation or perversion in the lower nature (for each of the three gunas has its divine counterpart in the higher nature). But tamas being the settled habit of the inferior nature tries to persist and keep or get back its place. That is the reason why this kind of alternation takes place between the two.