When we are practicing insight meditation, the mind will sometimes be subjected to various different negative conditions including sometimes sloth, torpor and laziness. The correct approach to this condition is to allow it to become our object of meditation.
Here is the Buddha’s guide to dealing with sluggishness:
“…on any occasion when the mind is sluggish, that is the right time to develop analysis of qualities as a factor for awakening, persistence as a factor for awakening, rapture as a factor for awakening. Why is that? The sluggish mind is easy to raise up by those mental qualities…”
Notice how your posture changes when you feel sluggish, whether the feeling is positive, negative or neutral, what thoughts arise to you when you feel tired. Do you have many thoughts or few thoughts? Are you talking yourself out of work or making excuses to avoid important tasks? Finally, notice how your body feels when you feel tired and where in the body you experience those feelings. In this way, you will become persistent in your meditation practice. You will develop the quality of analysis and experience rapture at the your new found understanding.