Aaaaaahhhhh....Oooooooh.....Mmmmmmmm

"Om expresses the four states of consciousness - jagrat (waking), swapna (dreaming), sushupti (deep sleep), and turiya (samadhi) - both visually and in sound. When we chant Om, each part vibrates in a different part of the body and represents a different state of consciousness. The Ah blooms in the lower abdomen and represents jagrat, the waking state. Oooh vibrates in the solar plexus and heart and represents swapna, the dream state. Mmm vibrates in our skull and represents sushupti, deep sleep. The fourth state, turiya, exists in the continuing vibration and resonating, unstruck sound of Om. Om is the sound that is God's name." - Summarized from the book Jivamukti Yoga by Sharon Gannon & David Life.