I am 27 (like Amy Winehouse and Janis Joplin were, ya know)... and I get these thoughts as well.

I remember in kindergarden me and couple other friends used to play game called "dying". I was obsessed with death since I can remember. Since my young days I wrote apocalyptic poems. I improved in form, the imagery stays the same. Every other day is an extra and over my time at this moment. I don't plan to go by my own doing at the moment (I am still keeping the option of "bailing out gracefully" open though).

Thing is... I am very much alive and there are times I am enjoying life. I guess thinking "whoa, I am ALIVE" is not normal... but that is how I feel at the moments. Awareness of my own mortality makes life strangely more enjoyable. It is a very comforming thought to me.

I am more worried about others than myself. I hate the thoughts of losing those who are close to me... my life? I don't care all that much about it.
(then again... there are times when I secretly hope for a disaster to strike us all and our civilization dying "like a beautiful flower").

so what I can recommend as somebody who goes "au naturale" route... get in peace with these thoughts and turn them into positive... yes, we will all die, but it means we were alive and it is sorta surreal miracle. For me, I would not want to get rid of this part of me... because life and death are very interconnected to me, just like light and dark.... the ying and yang thing.