This is, of course, dependent upon what one believes. But I can share with you what my belief is - the human (all living things for that matter) are made up of two life forces: the first being the physical body and the second being the soul or spirit. When someone dies it is their physical body that dies - not their soul/spirit. So their spirit moves on to the next dimension of life - some call it heaven - but I happen to believe there are many levels to the dimension without the physical body. The dimensional level the spirit ends up is based upon their learning, experience and knowledge - because each dimensional level is a new learning level.

Now for the question: are they aware they are actually dead? The answer to this question is yes, on the most part. But there are times, from my understanding and all the knowledge I've gained over the years is if someone dies suddenly and completely unexpectedly they can linger for a time because they are not aware they are dead. This is what is frequently considered a ghost. Ghosts are the result of many other things but this situation is not an uncommon one.