Some advaita teachers use the word “consciousness” to refer to mind consciousness (as in a person being ‘conscious’ of something) and “awareness” as something that is prior to that and universal.
One could surmise that while consciousness is Ātmā, awareness is Brahman or Paramātmā.
If awareness is the screen on which the movie of the world plays, the question often arises as to what happens to it when we are in deep sleep, in samadhi or when we are under the influence of anesthesia.
Instead of trying to answer the question myself, I will simply refer to an excerpt from the excellent Advaita Website maintained by Dennis Waite. I think the following resolves the question aptly.
Shankara uses the metaphor of the sun sending its light out in all directions. We need not be able to see the sun itself to know that it exists because, everything that we see, we see only by virtue of the sunlight reflected from it. Suppose that we are floating in the emptiness of space, with no objects, no planets or other opaque material, within the range of our eyes. If we were facing away from the sun then we would see only blackness. Although the light from the sun continues to stream outwards, there is nothing to illumine so that nothing is seen. And so it is with deep sleep. Although consciousness is still present (after all, it is our true nature), the mind and senses are effectively ‘switched off’. Consciousness itself is aware of nothing. It is the reflected consciousness in the mind that perceives objects via the senses. Since these are inactive, we are not aware of anything. But Consciousness is still there, as we realize on awakening because we know that we were aware of nothing whilst we were in the deep sleep state. This is why the Self is called the eternal witness or sAkshI; its ‘light’ is still there even in deep sleep.
Suppose that we have a dark, shuttered room. It is so dark that we are unable to find anything inside it. We are only able to open the door and, although there is bright sunlight outside, this does not penetrate far enough to illumine the interior. There is no electricity and I do not have a torch. I do, however, have a mirror. By positioning myself in the doorway, I can hold the mirror at such an angle that the sunlight reflects in the mirror and illumines the contents of the room. Although the mirror is itself inert, having no light of its own, it becomes a source of light by virtue of reflecting the light from the sun, which does have its own light. This, of course, is also how we get the moonlight by which we can see during the night, when there is a moon in a cloudless sky. The light of the moon is simply the reflected light of the sun.
The parallel can now be made with our own inert equipments and Consciousness. brahman is the equivalent of the sun, the only true ‘source’ of Consciousness. brahman ‘illumines’ the instrument of the mind, which itself is not a source of Consciousness. But, by virtue of this illumination, the mind is able to reflect the Consciousness via the senses into the ‘room’ of the world and become aware of the objects therein and interact with them (including the body-mind itself).
Furthermore, when we see an object, we register the object itself (i.e. its name, form and attributes) but rarely think that this is only possible because light is being reflected off it from an external source. Similarly, in respect of our actual awareness of objects or of our own body and mind, we register that we are aware of something but not thatby which we are aware, i.e. Consciousness itself. Once I have acknowledged that my feeling of being an aware, conscious being is because Consciousness is reflecting in my (independently) inert mind, I can also acknowledge that it is the same Consciousness reflecting in other independently inert minds that gives the impression of other people.