Majjhima Nikaya 2:118
SUJATOSantaṁ vā ajjhattaṁ thinamiddhaṁ ‘atthi me ajjhattaṁ thinamiddhan’ti pajānāti, asantaṁ vā ajjhattaṁ thinamiddhaṁ ‘natthi me ajjhattaṁ thinamiddhan’ti pajānāti, yathā ca anuppannassa thinamiddhassa uppādo hoti tañca pajānāti, yathā ca uppannassa thinamiddhassa pahānaṁ hoti tañca pajānāti, yathā ca pahīnassa thinamiddhassa āyatiṁ anuppādo hoti tañca pajānāti.
When they have dullness and drowsiness in them, they understand: ‘I have dullness and drowsiness in me.’ When they don’t have dullness and drowsiness in them, they understand: ‘I don’t have dullness and drowsiness in me.’ They understand how dullness and drowsiness arise; how, when they’ve already arisen, they’re given up; and how, once they’re given up, they don’t arise again in the future.