If I die suddenly, with heart failure or a beam falling on my head, there is immediate death. There is no fear; it is over. But give me an interval between now and dying, then that interval is fear. In that interval, I am afraid that my life will come to an end, so I am afraid. Thought, thinking about the future, what might happen, or thought thinking about the past breeds fear, conscious and unconscious. The unconscious is the residue stored by thought over centuries of time.