Why do Christians fear death

I always find it confusing when someone gets something like cancer that Christians pray for that person's recovery - especially if the person is elderly. That they don't want the person to die.

If you believe you're going to heaven, shouldn't you be excited to die and leave behind a world filled with suffering? Why aren't Christians *excited* when they are coming close to death?

I understand the fear of the actual process of death, and I understand that someone might worry about their loved ones they leave behind suffering.

But it seems to me that funerals should be much more upbeat than they are for Christians...