Is it normal that thinking about the distant future makes me cry?

Sometimes I just lay in bed for weeks at a time crying because I know that when all is said and done my life means nothing. Even if I contribute greatly to the world, even if I cure cancer or save all of humanity it will come to an end. Man is by nature, destructive, and we are on the path to our own self destruction. Even if somehow we over come this nature the sun will ensure the destruction of the solar system. If somehow we avoid that and propel ourselves into space in search of a new home the uncertainty of finding a place to prosper is high. But eventually our doom is certain. The universe continues to expand and it will not stop. In 10^64 years all matter is guaranteed to cease to exist (heat death of the universe). Not only is this the end of man but it is the end of life - everywhere; it is the end of knowledge and love and friendship and togetherness. It is the end of every idea any person has every had and the end of any possibility that a new idea could be generated. Is it normal to cry for days at a time because of this immutable fact?