Psychologically: A nightmare with relatively harmless meaning: One works off in it an experience with which one was a witness of an unfair process (often professionally or in the social sphere) in which some hopes or ideas were 'massacred' by several people. Or: A creative plan of a group was 'done in' by an envious person (or competitors). One would have had the possibility to undertake a little bit against it, however, it gave up from comfort (or conflict shyness). Now, nevertheless, the bad conscience torments and 'punishes' inactive watching with the massacre dream.