The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
10. In him who is senseless (in a swoon, &c.)
there is half-union; on account of this remaining (as the only possible hypothesis).
There now arises the question of what kind that state is which ordinarily is called a swoon or being stunned. Here the pûrvapakshin maintains that we know only of three states of the soul as long as it abides in a body, viz. the waking state, dreaming, and deep dreamless sleep; to which may be added, as a fourth state, the soul's passing out of the body. A fifth state is known neither from Sruti nor Smriti; hence what is called fainting must be one of the four states mentioned.--To this we make the following reply. In the first place a man lying in a swoon cannot be said to be awake; for he does not perceive external objects by means of his senses.--But, it might be objected, may not his case be analogous to that of the arrow-maker? Just as the man working at an arrow, although awake, is so intent on his arrow that he sees nothing else; so the man also who is stunned, e.g. by a blow, may be awake, but as his mind is concentrated on the sensation of pain caused by the blow of the club, he may not at the time perceive anything else.--No, we reply, the case is different, on account of the absence of consciousness. The arrow-maker says, 'For such a length of time I was aware of nothing but the arrow;' the man, on the other hand, who returns to consciousness from a swoon, says, 'For such a length of time I was shut up in blind darkness; I was conscious of nothing.'--A waking man, moreover, however much his mind may be concentrated on one object, keeps his body upright; while the body of a swooning person falls prostrate on the ground. Hence a man in a swoon is not awake.--Nor, in the second place, is he dreaming; because he is altogether unconscious.--Nor, in the third place, is he dead; for he continues to breathe and to be warm. When a man has become senseless and people are in doubt whether he be alive or dead, they touch the region of his heart, in order to ascertain whether warmth continues in his body or not, and put their hands to his nostrils to ascertain whether breathing goes on or not. If, then, they perceive
neither warmth nor breath, they conclude that he is dead, and carry off his body into the forest in order to burn it; if, on the other hand, they do perceive warmth and breath, they decide that he is not dead, and begin to sprinkle him with cold water so that he may recover consciousness.--That a man who has swooned away is not dead follows, moreover, from the fact of his rising again (to conscious life); for from Yama's realm none ever return.--Let us then say that a man who has swooned lies in deep sleep, as he is unconscious, and, at the same time, not dead!--No, we reply; this also is impossible, on account of the different characteristics of the two states. A man who has become senseless does sometimes not breathe for a long time; his body trembles; his face has a frightful expression; his eyes are staring wide open. The countenance of a sleeping person, on the other hand, is peaceful, he draws his breath at regular intervals; his eyes are closed, his body does not tremble. A sleeping person again may be waked by a gentle stroking with the hand; a person lying in a swoon not even by a blow with a club. Moreover, senselessness and sleep have different causes; the former is produced by a blow on the head with a club or the like, the latter by weariness. Nor, finally, is it the common opinion that stunned or swooning people are asleep.--It thus remains for us to assume that the state of senselessness (in swooning, &c.) is a half-union (or half-coincidence) 1, as it coincides in so far as it is an unconscious state and does not coincide in so far as it has different characteristics.--But how can absence of consciousness in a swoon, &c., be called half-coincidence (with deep sleep)? With regard to deep sleep scripture says, 'He becomes united with the True' (Kh. Up. VI, 8, 1); 'Then a thief is not a thief (Bri. Up. IV, 3, 22); 'Day and night do not pass that bank, nor old age, death, and grief, neither good nor evil deeds' (Kh. Up. VIII, 4, 1). For the good and evil deeds reach the soul in that way that there arise in it the ideas of being affected by pleasure or pain. Those ideas are absent in deep sleep, but
they are likewise absent in the case of a person lying in a swoon; hence we must maintain that, on account of the cessation of the limiting adjuncts, in the case of a senseless person as well as of one asleep, complete union takes place, not only half-union.--To this we make the following reply.--We do not mean to say that in the case of a man who lies in a swoon the soul becomes half united with Brahman; but rather that senselessness belongs with one half to the side of deep sleep, with the other half to the side of the other state (i.e. death). In how far it is equal and not equal to sleep has already been shown. It belongs to death in so far as it is the door of death. If there remains (unrequited) work of the soul, speech and mind return (to the senseless person); if no work remains, breath and warmth depart from him. Therefore those who know Brahman declare a swoon and the like to be a half-union.--The objection that no fifth state is commonly acknowledged, is without much weight; for as that state occurs occasionally only it may not be generally known. All the same it is known from ordinary experience as well as from the âyurveda (medicine). That it is not considered a separate fifth state is due to its being avowedly compounded of other states.
151:1 Viz. with deep sleep, as will be explained below.