The Mandukya Upanishad deals with the four states of consciousness.
- Waking, 2. dreaming, 3. Deep sleep and 4. Turiya or samadhi state. It also states that everything in the universe is OM and that the past, present and future are contained in OM. The three components or syllables comprise the three states of Brahman. After meditation on OM one is taken to the silence which is Atman or Brahman.