Fear of death is inherent in us biologically, he is part of the innate behaviors of any living creature of instinct. Due to this instinct we in case of danger will take all reasonable measures to avoid, to escape.
If we were not afraid to die, they often do dangerous things very lightly. We would take more risk, not thinking about the consequences of our actions. Mankind would simply become extinct.
However, the fear of death in a human being is not only a biological mechanism that promotes survival. Death for man is a tragedy. For many people the thought of waiting for their death, so great and terrible that they try these ideas to avoid.
What caused this horror?
The reason is fear of death that we don't know what awaits us after death. The unknown frightens always, like a small child afraid of the dark because he doesn't know what it is - and suddenly the danger?
Death is the most important change in our lives. In death, life in the usual sense ends. Everyone is afraid of change, and this change is final, irreversible and incomprehensible.
For people who believe death is not so mysterious as to atheists. For the believer, the end of earthly life is not the emptiness and nothingness, it is the end of physical life, the beginning of the state in which the soul exists apart from the body. Death is the birth of earthly life into eternity, the beginning of eternal life. For Christians, for example, death is the awakening of the soul in Another world, where she resides or with God or without him - depending on how one has lived his life on earth, righteously or sinfully. And so the whole life of a believer is, by and large, a preparation for death.
Death gives life to any human sense. The realization that our life on earth is not eternal, gives people an incentive to rush to do good and avoid evil, to love and cherish life, every moment.
By the way...
Small children are not afraid of death. Of course, they know what death is, they are confronted with it in their lives, but they do not see death as something that relates to them personally. Every child thinks that he is special, and that he will live forever. The moment when a child realizes that he will die once, usually around the age of 6 years. And becomes a real shock for him. Through it passes each of us.
What is death? Why do people die?