I saw a lot of people in this thread talking about death and the concept of non-existence earlier on. I've been thinking a lot about this recently, and as superfly9 said, sometimes feel a sense of panic at the thought of non-existence.
It's not like I've never thought of this concept before, and as a matter of fact, I thought I'd completely come to terms with death and gotten over the fear of it. However, a certain experience I had caused me rethink my lack of fear.
Every day when I was finished with work, and walking back to my car waiting in the parking lot, I would reflect on the time I spent at my job. In those few seconds of me walking to my car, the ten hours I spent in the building behind me seemed like no time at all, because that time was all over. As days passed, I began thinking about applying that same feeling, but to a lifetime instead of a work shift.
The thought of the end of my existence, and looking back on my life took on a new form of discomfort to me, because of this new way I had of looking at it. I even wrote down a quote I invented that sums up the idea. "It took a decade to happen, but a second to remember."
So I suppose that I'm not necessarily afraid of death, or the infinite unconsciousness that comes with it. I just get scared knowing that there will be a time in the future when I have no recollection of my life and never will, for I will never return. Like it never even happened.
However, an interesting thought came to mind.
What is it like to go to sleep, and never wake up? Also, what is it like to wake up, after never having gone to sleep? The process of being born and dying.
If you cannot experience the passing of time when you are dead, then the only possible thing that could ever happen, is the same thing that happened when you were born. You wouldn't even need to wait for it, as nature abhors an experience of nothing.
That's probably not going to happen though.
Great video for anyone interested in the subject: