[637] "He purifies the mind (citta) from dullness and drowsiness (thīna-middha)": there is dullness (thīna); there is drowsiness (middha).
Herein, what is dullness?
That which is indisposition of the mind … the dulled state of the mind — this is called dullness.
Herein, what is drowsiness?
That which is indisposition of the body … the state of sleep — this is called drowsiness.
Herein, what is the mind?
That which is mind, mentality (mano), mentation (mānasa) … the corresponding mind-consciousness element (mano-viññāṇa-dhātu) — this is called the mind.
He cleanses this mind of this dullness and drowsiness, cleanses it thoroughly, purifies it; he frees it, releases it, delivers it completely. Therefore it is said: "he purifies the mind from dullness and drowsiness."
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.