In the meditative concentration with initial application and sustained examination (vitarka-vicāra), it is precisely the time to investigate Chan.

Question: In shallow meditative concentration, one lets the mind consciousness and the manas remain in a very keen state of sustained examination (vicāra). In this keen state of sustained examination, one feels as if one can faintly "see" one's own body, and can keenly perceive subtle events occurring within tens of meters around. When the conscious mind is in the state of sustained examination, it means: both the mind consciousness and the manas are highly concentrated, passively perceiving what is happening around, but the conscious mind does not deliberately attend to or discern the events taking place; it merely knows that the events are occurring, similar to the state of "watching coldly from the sidelines without stirring thoughts." Is this state in accord with the Dharma? 

Answer: The state of sustained examination is of course meditative concentration (samādhi), and not shallow concentration at that. The state of initial application (vitarka) is also concentration, but shallower, because the mind stirs more. In the state of sustained examination, the mind does not stir yet has knowing; over time, wisdom-based cognition of the known will arise, and one can see through the dharmas that are known, knowing that dharmas are empty; then the mind becomes empty, thereby reaching the state of equanimity. Both initial application and sustained examination have an object, and the object must be single-pointed for meditative concentration to appear. Some states of concentration lack wisdom, while some states of concentration contain wisdom; only when there is an object of contemplation (ālambana) within concentration is there wisdom; otherwise there is no wisdom—it is pure concentration. Both initial application and sustained examination are lucid concentration and both belong to right concentration. However, at the stage of initial application, concentration is shallow and the mind stirs much, lacking sufficient stillness. The state of sustained examination is the later stage of investigating Chan, the state in which wisdom most easily arises. At this time it is the stage of deliberation (manana) led primarily by the manas, with the mind consciousness not moving, or moving only slightly and mildly. 

Question: If one maintains this state of "sustained examination" in a very quiet environment, one will gradually feel as if the surrounding space and time have congealed, the body seems to be barely there, and the conscious mind seems to float outside the body, quietly "perceiving" everything. After emerging from this state, one finds that one's thinking power and perceptive ability are considerably stronger than usual—perhaps this is an effect brought about by the conscious mind maintaining concentration? As the duration of this state of "sustained examination" gradually lengthens, one finds that the concentration of the mind consciousness and the manas grows ever greater, and the power of awareness becomes ever keener. One also finds that breathing and heartbeat become slower and slower, finer and longer, and one truly worries that at some moment the breathing and heartbeat will cease and one will die. 

Answer: In the state of sustained examination, the mind consciousness maintains only a knowing, without extraneous thoughts; the manas is undisturbed and will thus engage in deep, subtle, and single-pointed deliberation, and wisdom easily arises. Once the wisdom of the manas arises, one can see through the object-contemplated realm and see its emptiness, and it becomes easy to realize the Path. If the state of sustained examination has not been reached, the mind consciousness's thinking is active, and the manas's deliberation will be obstructed, so no true wisdom arises. The results that the mind consciousness derives through thinking, inference, analysis, and judgment will not be deposited into the manas; the manas does not accept them. Then no matter what views this person's mind consciousness holds, in the end views remain views and mental conduct remains mental conduct, with no interaction between them, and one's practice still does not get on the Path. Look at how many people claim to have attained the fruits, seen their true mind, and so on, yet their body, mind, and world have not changed in the slightest; on the contrary, their afflictions grow heavier and heavier, and their pride blazes even more fiercely. That is because the mind consciousness has analyzed and reasoned out a principle, but the manas does not accept it; what they think and do remains as before—still the same old person with the same old conduct. The name is the name of a sage, but the mind is the mind of an ordinary being. Then they one after another regress and fall away from the Path—how pitiable.