Om is the all encompassing cosmic vibration of the universe.
The top curve denotes the state of deep sleep. This is where the sleeper is subconsciously shut down, desiring nothing and having no dreams.
Represented by the large curve, this state of consciousness is turned outwards and experiences the world through the five senses. This is the most common state of human consciousness.
The dot signifies the fourth state of consciousness. In this state, the consciousness looks neither outwards nor inwards. This utterly quiet, peaceful and blissful state is the ultimate aim of all spiritual activity.
This is what gets in the way of our spiritual development, preventing us from realization of the highest state of bliss (the dot above this curve). this semi-circle doesn’t touch the dot, meaning that the highest state of consciousness is unaffected by Maya.
The middle curve, which lies between deep sleep and the walking state signifies the dream state. In this state the consciousness is turned within, and the dreamer experiences a world behind closed eyes.