Analysts say that the reason for North Korea's attack is because of its "growing frustration toward the conservative South Korean government as well as the need to hold one-on-one talks with Washington for aid." I think it is much simpler. The South Korean navy did suspicious military exercises in waters they know to be disputed. Do they really expect North Korea to ignore such a blatantly arrogant move?
And now the the South Korean government announced that it may retaliate by shooting at the North Korean missile launch base. If this kind of tit-for-tat mentality continues it might escalate into something truly unpleasant. Since the current South Korean president has been in office, the tension between the two Koreas have risen uncomfortably. Is this part of some greater strategy he has? I don't think it is working.
As for my worried family and friends, do not stress too much.