This Upanishad is derived from the Atharvaveda. It is the shortest of all the Upanishads, consisting of only twelve sentences. The name Mandukya Upanishad means the scripture of the Toad. This may be because it is said that the God Of water, Varuna took the form of a toad to impart this Upanishad. There is also another belief that the Upanishad was the work of a sage known as Manduka.
The Upanishad explains the OM or Aum, the Universe, the Self, and the Supreme Being. It shows how these four relate to each other. It also specifies the four states of the consciousness. According to the Upanishad, these four are the waking, the dream, the deep sleep and the transcendental consciousness. In the waking state the human is aware of the physical world. The second state, which is of the dream, is in which the mind is awake while the body sleeps. In the deep sleep, both the body and mind are sleeping but still there is awareness of the sleep. The fourth is above all the other three. This is the state of consciousness where the Self is aware of everything and is not attracted to or disturbed or distracted by anything. This state alone is the real and true state.
Each of the letters of Aum applies to these four states. The fourth is wordless or the Incommunicable. It is said that this Upanishad leads one to salvation or to the transcendental consciousness free from the chains of desire, thought or action, unified with the Supreme Being.