Getting attached to the pleasant feeling experienced when the mind is concentrated is clearly a potential problem. How do you react if someone or something rouses you from your tranquillity, e.g. by banging a door, etc.?
Drowsiness is a hindrance. If the mind becomes dull, get up and do some walking meditation. It is recommended to alternate walking with sitting to balance the energies. Excessive energy will lead to restlessness, while excessive concentration will lead to drowsiness.
Like drowsiness, restlessness is just another one of the five hindrances. It should be observed and contemplated as “Restless, restless,” until it disappears. Drowsiness is somewhat difficult to note clearly and precisely, because the mind is dull.
• • • • (Upasampadā: 24th June, 1979)