Answer:
Hamlet means that he's worried that, even in death, he might still be disturbed by dreams of his earthly troubles. In this famous soliloquy, which begins "To be, or not to be," Hamlet weighs up the pros and cons of committing s**cide or facing up to one's troubles. He realizes that the possibility of being tormented by dreams even after death is one of the downsides to taking your own life.