This question was really hard for me, there's almost nothing what can make me fear and that dont means that I'm braveheart or someone like that, just I'm realist and looking at everything in this way, I don't believe in life after death, but why I should fear of death? It's inevitably and some day it happens. what can terrorize more than death?
...Well there is one thing...
So what can it be? Ok I'll explain. As you may know or not I'm biologist, I learned biology and other scienctific disciplies deep and it caused my love of life and nature, all biological life in the earth and I hope in other planets too. Life is amazing and unexplained thing,for us it is usual because we see it everyday But imagine yourself in mars where you are standing lonely with our robots - ''spirit" and "opportunity" and nothing alive around...I think that's what terorizes me - emptyness where nothing is alive, we don't appreciating life everydey, but it's major treasure what we have on earth and maybe in whole universe. Sad fact - one day it may happen, with help of human or some cosmic cataclysm,and we will lost most valued thing in universe - Biological life