Now, the world can be divided into four separate 'layers' stacked upon one another in successive coherence and discretion of detail. This is a most convenient fiction, as the actual metaphysical structure of these 'layers' are couched in terms of older psychology, and thus take their shape as is easiest to describe. In reality they are enmeshed, with inconsistent borders, feeding into and out of one another.
The Zeroth Layer, the Conscious, the 'Real World' the space where all waking beings reside is topmost, filled with all the known universe. It is a layer of sensory perception filtered through mechanisms of rationality by brains, a layer of distinct wavelengths, atoms, pressures, materials, and elements that obey four basic constants—in short, it is very constructed and ordered by the observations of its inhabitants. In a way this is both its greatest gift and limitation: assumption and law have events far less mutable, with abnormalities reasoned away or too minuscule or obscure to make much impact on a large-scale. But likewise this keeps it largely intact.
The First Layer, the Personal Subconscious, the 'Shallow Dream', the trillions of individual subconsciousnesses that are formed by just as many brains, all clustered together as grains of sand. The First is a kind of warped reflection of the Zeroth, holding the minds as the latter holds the brains: each metaphorical grain of sand is all the perceptions, impressions, reactions, mid-level data, and subtle computing made law in its own small space. In sleep, the conscious mind reduces itself and allows for a more direct connection with subconscious thought—this connection between the physical and metaphysical results in dreams.
Each subconscious in the First Layer is very private, near-impermeable if not for how they tend to bottom-out and leak into the Second Layer or make themselves subject through physical manifestations in art and thought and behavior.
The Second Layer, the Collective Subconscious, the 'Deep Dream', is simultaneously that amassed pool of leakage from the First, and its own kind of template by which the shape of the First is taken. Within it are primordial swathes of common-knowledge, patterns of habit and law that can be observed in all beings—communication techniques, emotional reactions, fears and counter-fears, needs and compulsions, the base stuff of the mind—with stains of the nuanced individual minds from above. These large patterns allow it to be more navigable than the First Layer, and even the Zeroth, for it informs both while being informed.
The Third Layer, the Template Subconscious, the 'Waste Land', is a mysterious, somewhat-theoretical Layer. Going by the model of the above two Layers, each progressing towards primordial form, the Third thus must inform the Second by being the template on which patterns of all minds can form; that is, it must be the most base of all, with a blank structure that allows for the above Layers to be constructed atop it. This makes it most dangerous, for to imprint a structure or pattern upon it would be to utterly alter the structures of other Layers.
Subsequent Layers either do not exist, or are so base and simple as to not allow definition beyond their existence allowing the existence of all above.