Does sleep = consciousness, unconsciousness or something else? Among the various definitions of the word consciousness is awareness, with wakefulness a general synonym.

If someone hits you over the head, knocking you unconsciousness (though still alive), then you're said to be unconscious. But are you also considered to be unconscious when you're sleeping?

One of the key differences (for me) is that a sleeping person can typically react to an alarm clock, whereas a person who has been rendered unconscious through an injury is effectively dead to the world.

If sleep is NOT a form of unconsciousness, what is it? Is a sleeping person still conscious, or is there another term to describe it?
The dictionary definition  of "unconscious" is to not be capable of conscious thought, ie, be asleep and unaware. Technically, you are unconscious when you are asleep.

When you get knocked out ie. a concussion, it is thought that the forces from the injury disrupt the normal cellular activities in the reticular activating system located in the areas impacted and that this disruption produces the loss of consciousness. 

Terminology wise, I believe this would be considered a temporary coma. (The definition of a coma is: a state of unconsciousness in which a person: cannot be awakened; fails to respond normally to painful stimuli, light, or sound; lacks a normal wake-sleep cycle; and does not initiate voluntary actions.)