About This Answer
A meditator describes the mind becoming very sharp, then a sense of emptiness, sometimes darkness, and moments of feeling as if they were not there, beyond their control. Ajahn Dtun explains that when the mind seems to go away and come back, it is a lapse of mindfulness. One must keep working to keep the mind centred in the present moment. If the mind is very peaceful it will put down the breath, and then one simply keeps mindfulness focused in the present.
The questioner then asks whether, in deep concentration with no thoughts, they should contemplate the Dhamma or simply rest. The time for developing insight, he answers, is when the mind begins to withdraw from that peaceful state and thinking resumes. While it is peaceful, allow it to rest for as long as it wants to stay. It is like someone sleeping: you let them rest, and it is after waking that they work.