यदग्रे चानुबन्धे च सुखं मोहनमात्मनः। निद्रालस्यप्रमादोत्थं तत्तामसमुदाहृतम् ॥

yad agre chānubandhe cha sukhaṁ mohanam ātmanaḥ nidrālasya-pramādotthaṁ tat tāmasam udāhṛitam

That pleasure which both at first and afterwards is delusive of the self, arising from sleep, indolence and heedlessness, that is declared dark.

In plain words: Krishna says the lowest, "dark" kind of pleasure fools a person from start to finish. It comes from too much sleep, laziness and carelessness.