It is a highly developed way of thinking of the Upaniṣads that death is observed as an extension of sleep. When a man sleeps, the vital functions around breath suspend, when he wakes they activate, and they take their departure (from his body) towards the next world when he is dying. The breath is a marker identifying his state of being dead or alive. Now, the consecration (dīkṣā) in the Agniṣṭoma has descriptions of “sleep” in which the consecrated sacrificer who has been awakened from a temporary sleep says the mantra claiming a secure return of the vital functions, including the breath. The Śathapatha-Brāhmaṇa, however, in opposition to the mantra, proclaims that the breath will not take departure from the sleeping (living) sacrificer, and it shows, as it were, the embryonic phase of the theory of the vital functions around sleep and death which held sway in the era of the Upaniṣads. Furthermore, this mantra is applied to another ritual called Sāvitra-Cayana, a variation for the piling up of the fire-altar for the Agnicayana of the Taittirīya lineage. It acts as a mantra preventing “death” and ensuring the recovery of the vital functions from “death.” Therefore, the mantra can be considered a good example of the Vedic way of thinking of the vital functions as mediators between sleep and death as this developed from the Brāhmaṇas to the Upaniṣads, i.e. from ritualistic thought to philosophy in general.
