I keep having these dreams about the world ending. Usually it's either some kind of natural disaster that starts or then it's zombies. I'm 25 years old, so I shouldn't be having these, should I? What's the purpose of these dreams and why do they keep coming back?

The weird thing is that last night the dream ended with me saying goodbye 2 someone completely stranger on the phone, just before the world was about to end. It wasn't a family member, nor my lover, just some random person who I happened to talk with. Usually these dreams involve me running around trying to save my family, but not this one.