Scientists have come up with many theory’s as to why we dream, and a nightmare is just that, a dream. Unfortunately, they’ve found no proof as to why we dream. Some suggest that we dream to eliminate the stress from our everyday lives. Try taking up meditation or yoga to eliminate stress or keep a journal of things that are upsetting to you as a means to let it all out. If this doesn’t help then seeking the advice of a councilor might also be beneficial.