Consciousness, Sleep, Coma, and Death

The degree of our conscious awareness depends upon status of our brain function. When the brain is fully functional, the brain is in full control of our bodies and a full state of consciousness is possible. However, if the brain is damaged, functionality of the brain can be greatly reduced to result in a coma in which no consciousness awareness or response to external stimuli is present. The most severe for of coma leaves the afflicted in a vegetative state with very limited brain activity. Recovery of full brain function is possible. But when all the brain cells die, all brain function, including that of consciousness awareness or response to external stimuli cease and the person is irreversibly dead. 

Interestingly, consciousness awareness can be lost in a fully function brain. Indeed, the brain simply does not pass about 90% of all brain awareness of sensory inputs along the conscious mind. Similarly, when sleeping, nearly all brain awareness of sensory inputs is not passed along the conscious mind. But some brain awareness -- say, a loud noise -- may result wakefulness and conscious awareness in the mind.

Consider that conscious aware arising from sensory data harvested from the world around us by way of our physical brain is our only means of mentally experiencing our existence, we surely do miss a great deal of the reality our our existence. Yet the process of  evolution has enabled just enough conscious awareness of it to sustain and propagate the life of the species. Indeed, you are the continuation of an uninterrupted series of living cells that date back millions, if not billions, of years. And, in your case, the series only ends when your brain and all the other cells in your body are dead.