Well, I'll go reeeeeeeeaaaaaaally deep into this. XD
If the world was ending... why should it end? Is this the apocolypse of the Bible, the Mayan thing, or something else completely? If it's like what the chapter Revelations says it'll be like, well, I would be panicking first. Because I wouldn't know what to do and who I was anymore and if I really was God's child or not and if God would accept me and forgive my sins and all that other stuffs. First major reaction.
Next I would pray. Because I would naturally do that.
Then I would find a way to hide from Satan and possibly go through ideas in my head to make him get away from me if he did see me.
After that I would most likely find a way to stop the war between "Gog and Magog", because I hate wars. Sooooo very much.
And theeeeeeeen... I really have no idea. XD
But if it was nothing like that, well, it still depends. The sun's exploding into a supernova or eating us as it expands into a red giant? I really don't know what I would do then. Humanity ends due to an epic war or a meteor colliding or some other thing like that? Still dunno. And if I die before the end of the world?
I would be dead already, so meh.
Oh, I only have six hours to live? Well meh. I guess if I knew that, I would be able to survive those six hours by just playing musics on my piano. Because if I didn't, I would seriously be contemplating suicide if I knew my life was about to end in six hours. And knowing that would be pure agony for me. x_x
Yeah, I'm weird. XD