Mandu K: At one point the sense of reality must have shifted from that to this. This shifting cannot happen without even a flash of deep sleep in between, where one is let go off and you catch the otherOne. From the deep sleep perspective, Mandu K says both are dreams.
Swami Sarvapriyananda teaches one of the shortest and most profound upanishads accompanied by Gaudapada's Karika. This lecture covers Karika 1-5.