The clear take home is that a nightmare is simply a message from your subconscious or whatever to address some aspect of your life and to take it seriously. I think that is actually true although I cannot seriously vouch for all that.
Whenever any dream is remembered, it is an indication that the waking mind has a creative, transformative role to play in the evolution of whatever issue the dream is presenting. For millions of years, the ability to pay immediate and focused attention to nasty, threatening stuff has been a primary survival test. The creatures who pay effective attention to threats tend to survive, and the ones who don’t tend not to survive. In this way, we have been shaped by natural selection to be inherently predisposed to pay attention to ugly, scary, and menacing experiences.