I know I’m alive at this very moment because I am conscious of me living. I know I’m in a room because my brain knows that a room should contain enclosing barriers, so it uses my senses to identify the tall, flat, long and thin structures surrounding me as walls, which were placed there to serve as an enclosure. I know this room is mine because my brain understands the concept of property, and it remembers that I’ve spent a lot of time here, and that my mother told me that it is my property. I identify my current actions as typing because my brain is comparing the similarity of my actions to those I’ve assigned to what can be considered ‘typing’. Therefore, you know where you are and what you are doing because you recognize the fundamentals of it.
If however I am not conscious, I am not aware of my actions nor of my surroundings. When asleep, I am not conscious of the fact that I’m busy sleeping, nor am I aware that I’m not awake. I only know I’m sleeping when I become conscious of it inside a dream, and I only know I’ve been asleep once I regain consciousness and my brain recalls the sensation of awakening. I’m only aware of my existence once my brain has proven that I am indeed existing.
I consider death to be when you no longer have the ability to prove your existence to yourself. I therefore don’t know I’m not dead unless I prove it to myself.
That is why sleep can be so scary. You step into this void of non-existence until you awaken on the other side. Up until that point you have no way of checking if you’re still a part of the living.