The twelfth mantra, the final mantra will come where it will speak about the silence. The silence pure consciousness is what we really are in which all these experiences appear. This whole ome meditation is not really the central teaching of the Upanishads on this side of the chart. It's called Waker Dreamer Deep Sleeper and Turiam by Sri Suddha Ma Surya Turiam.
Swami Sarvapriyananda teaches one of the shortest and most profound upanishads accompanied by Gaudapada's Karika. This lecture covers Karika 22-23 and Mantra 12.