Nightmare wasn't all evil as monsters and humans thought. He was nice and loving like dream, he just couldn't give out good dream and good vibes to everyone only bad vibes and nightmares. He never loved the way he was, he wanted to be more like dream so everyone could be loved more and go anywhere he wanted.
He wanted to die! he didn't want to stay in this world anymore!!! so he made a date and time when he kills his own self! 5 days...5 days...
that was the deadline 5 days before he kills himself. but when dream gets in the way and tries to cheer him up...
would he keep the deadline?