The mental process which rests on the notion of non-existence is sleep
This is a special notion arising from the recollection on waking in the form of ‘I slept well; my mind is calm and has cleared up my understanding’, or else ‘I slept badly, my mind is dull and wanders aimlessly’ or again ‘I slept sunk in stupor; my limbs seem heavy and my mind is limp and faint, as if some force had seized control of it.’ There would be no recollection on waking unless caused by an experience; without an experience there would be no memories based on it and corresponding to it. Therefore sleep is a particular notion, and like all the others it is to be inhibited in samādhi.
Now the sūtra describes sleep: The mental process which rests on the notion of nonexistence is sleep (nidrā). Right knowledge, illusion, and logical construction, which have just been explained, are in the waking condition, and sleep begins when they cease; so sleep is now described, immediately after them.
Non-existence means absence of the waking state, not absolute non-existence, because there could be no notion of that. The notion of non-existence means that there is a notion about non-existence. The mental process of which this is the support is one which rests on the notion of non-existence, and that is sleep (nidrā), a dreamless state (suṣupta-avasthā).
(Opponent) The dreaming state (svapna-avasthā) also must be included in sleep.
(Answer) It does not come under sleep as defined here, because the sūtra (I.38) will distinguish them: Or by meditation on the knowledge of dream (svapna) and sleep (nidrā). There sleep (nidrā) refers only to dreamless sleep. It is only dreamless sleep that rests on the notion of non-existence. Dreaming does not rest on that notion, but on memory, and memory is of something experienced. The commentator illustrates this point about memory when he says that in dream, things remembered become actualized (comm. to sūtra I.11).
It is evident that dream is a mental process, and there is no doubt about that. But the question does arise about dreamless sleep, and so the commentator says, Dreamless sleep is a special notion arising from the recollection on waking. Unless there had been a notion, there could hardly be a recollection. And when one wakes, one does recall, ‘I have slept well’ and so on. The recollection itself is a reflection of the notion that I have experienced something; unless there had been some experience, that reflection would not be there, nor could there reasonably be any memories about it. If dreamless sleep were not a notion, there would not be any effects or notional experiences such as my mind has cleared up my understanding (of a problem), where mind is active.
Again, there is the experience I slept badly, my mind is dull, static, ineffective; or again My limbs seem heavy (guruguru) – following the sūtra 8.1.12 of the grammarian, the repetition of the word indicates some resemblance, so that the meaning is that they feel heavyish; my mind is limp, as if some force had seized control of it out of my possession, as it were. There are these various memories, effects and recollections, and the commentator has presented three of them by which it is established that sleep is a particular notion.
Again, a man who has been asleep in an inner room, without any hint from outside however slight, has recollected immediately on waking ‘I have slept a long time’, and this would otherwise be inexplicable.
(Opponent) These are not memories, because a memory must be of some particular thing which one has experienced, whereas on waking from dreamless sleep one does not remember any definite thing.
(Answer) In the infant as soon as he is born, we see the desire for union with the breast, which he has never experienced in this life. It is not something automatic; purposeful activity is always consequent on some memory, as we see in adults. So here, the recollection whose object is dreamless sleep must follow from some notion just because it is a recollection, like recollections of what has been perceived in the waking state. The heaviness of limb and so on of a man waking from dreamless sleep is an effect, preceded by some experience of discomfort or the like; the heaviness is an effect in its field, the limb. Just as it is certain that this effect has been preceded by some experience of discomfort, so it is certain that sleep is a special notion.