Consciousness and Sleep
Why do we say that a person is unconscious when asleep but conscious when awake? During sleep we often dream and dreaming is a conscious activity of mind, so why don’t we say that we are often conscious while sleep? Why do we speak as if sleeping and consciousness are opposed? Similarly, why do we suppose that being awake rules out being unconscious? It doesn’t rule out the existence of unconscious mental activity, so why should it rule out being simply unconscious—no conscious mental activity at all? Couldn’t a person be awake in the normal sense—mobile, eyes open, and alert—and yet there is a break in consciousness, a gap in the stream? Couldn’t wakefulness be punctuated by periods of unconsciousness, as sleep is punctuated by periods of consciousness? Couldn’t someone go into blindsight mode every once in a while and still be said to be awake?
Part of the problem is defining what it is to be awake or asleep. The OED defines “sleep” as follows: “a regularly occurring condition of body and mind in which the nervous system is inactive, the eyes closed, the postural muscles relaxed, and consciousness practically suspended”; while “awake” is defined simply as “not asleep”.  But couldn’t these conditions for sleep be met and yet the person (or animal) is still awake? What if I relax on my bed with my eyes closed and think only of sheep—aren’t I still awake? What if I take a drug that cuts off sense perception, paralyzes me, and leaves me with only the most minimal consciousness—could I not still be awake? And what about the clause about consciousness being “practically suspended”? It doesn’t seem at all suspended during an intense nightmare or an ardent erotic dream. I suspect the editors mean “consciousness of the environment”, but that is neither necessary nor sufficient for being asleep: you can be asleep and aware of outside stimuli to some degree (hence the qualification “practically”), and you can be wide awake while having no awareness of the environment but only of yourself. Clearly, we have poor definitions of what sleep is, and likewise wakefulness. We don’t have a good analysis of what these states involve.
The point remains that the logical connections between “asleep” and “unconscious” and “awake” and “conscious” are opaque at best. There seem in fact to be no logical connections here: we can experience states of consciousness during sleep, i.e. dreams, and we could go consciously blank while awake, i.e. not asleep. Being asleep is roughly a state involving being relatively unreceptive to the environment, but that doesn’t preclude a vivid inner consciousness such as occurs in dreams. Being awake is roughly being alert to the environment, immersed in it, but that doesn’t preclude moments of conscious blankness, as in blindsight. We say of simple organisms such as insects that they are awake, i.e. not asleep, but we don’t take this to entail that they are sentient beings. So there appears to be no analytic or necessary link between the awake/asleep distinction and the conscious/unconscious distinction. Indeed we could invert our usage and incur no charge of logical infelicity: we could say that we are conscious while asleep (though not all the time) and that we are unconscious while awake (though not all the time)—that is, we could say the latter if we actually had periods of conscious blankness while awake. Just as we are sometimes conscious during sleep, so that sleep is not necessarily a time of unconsciousness, so we could sometimes be mere zombies while awake, so that being awake is not necessarily a time of (uninterrupted) consciousness. You can be lying down in the dark fast asleep and have conscious experiences inwardly, and you could be moving around the world completely awake (“not asleep”) and be experiencing nothing consciously at all—you are in your robot phase. As things are, we are (apparently) conscious during the entirety of wakefulness—though there might be brief unconscious interstices—but we could be only intermittently conscious, perhaps so as to relieve the consciousness centers of our brain. Thus it would be arbitrary to say that we are unconscious while asleep and conscious while awake; rather, we are conscious and unconscious in both conditions (though not at the same time). I therefore recommend that we stop speaking as we normally do: we can be asleep or awake (whatever exactly these conditions amount to) and we can be conscious or unconscious, but there is no logical connection between these two dichotomies. Someone could in principle be continuously conscious during sleep by dreaming all the while, and could be continuously unconscious while awake by going into total zombie mode. Thus you could be completely conscious while asleep at night and completely unconscious while awake during the day—you could invert the normal human pattern. You could wake up to unconsciousness and go to sleep to consciousness. Your consciousness could be completely devoted to dream consciousness, while the banalities of waking life are handled by an unconscious brain system. For a possible species this might be an efficient way to apportion consciousness. Why waste your consciousness resources on fact when fantasy is so much more interesting? Sleeping is the time to let your consciousness roam free; being awake can be consigned to unconscious brain mechanisms. 
 It is an interesting question whether there is any viable definition of “awake” that defines it more positively. The dictionary editors seem to be of the opinion that asleep is the more basic concept, with awake defined simply as its negation. This is to treat awake as what I elsewhere call an essentially negative concept. I suspect they are right to do so: our concept of wakefulness just is the concept of not being asleep.