Why doesn't Caesar sleep well on the eve of the Ides of March?

Caesar had previously been warned by a soothsayer that he would be in grave danger until the passing of the Ides of March. This of course is the reason he didn't sleep well as it lurked in the back of his mind. When one of his companions reminded him of her words on the day of his death he replied, "they have not gone yet." I guess he was right to worry.

This night also produces a terrible storm, which the Romans viewed as a predicator of bad things to come, as well as Calpurnia's dream that caused her to cry out in her sleep three times:

      CAESAR   

      Nor heaven nor earth have been at peace to-night:   

      Thrice hath Calpurnia in her sleep cried out,   

      "Help, ho! they murder Caesar!"