Or do we just fear the pain that usually come with it?

Some animals don't seem to care about death and sacrifice themselves willingly to ensure the survival or their colony/offsprings
Do you think an antelope flees from a lion because it know it means "death" or because it knows it will suffer a gruesome one?

Our own cells are programmed to commit sudoku if they become a danger for the rest

So why do you think this fear is pre-programmed within our brains?