To further expand on "don't worry about it unless it's your job to":

Unless you are able to directly exercise nonzero control over the foreign policy of a nuclear power, the threat of a nuclear apocalypse is sufficiently far removed from anything you can do anything about, that it's tantamount to worrying about a large asteroid impacting the earth. It would be devastating, sure, but it's not productive to genuinely concern yourself with it, because it's unlikely you'll survive and there's not much you can do to change the likelihood of the event or your survival.