Christians why are you all scared of dying?

I'm agnostic, but I totally open to believing the possibility of a heaven. The thought of dying scares me, because of my mind going blank, without thought for all eternity. Now I'm pretty sure most Christians are also scared and saddened by death, but why. If you are so sure, about heaven and that if you are a good Christian eternal joy awaits, why are you also scared and saddened by death?