[TriNetra]

At the core, we are pure awareness devoid of any object (thoughts). We can direct this awareness which we call the art of attention. We're pure awareness and we decide to attend something. However, to attend and receive information from the physical plane, we need appropriate instruments. Brains and its organs of senses are those instruments. If these instruments have fault, obviously we as awareness don't receive enough information and it seems our consciousness is reduced. In waking state, we receive info from physical senses. In dream state, these senses are in suspended mode but mind is active in imagining the experiences in a virtual world and hence awareness has an instrument. In deep sleep, even mind is in a state of rest and hence awareness has almost no active instrument. Still, we awareness does exist and thus we know that we had a good or bad sleep when we wake up.

[placebo]

I doubt the fact that we know we've had a good or bad sleep is related to the existence of awareness when in deep sleep. If someone remains indefinitely in deep sleep there will be no personal experience and therefore nothing to qualify as good or bad. When a sense of self returns with waking up then your body gives you the signals from the accumulated effects that you didn't sleep in a good position or whatever positive or negative aspect that has left a trace while you were out cold.

I'm not negating the possibility that consciousness might be a primary aspect of existence - it's just that if that is the case then it is not something you have or can remember. It would be more accurate to say that it is something that has you, and as some spiritual masters would point out, it would be even more accurate not to say anything about it :)