Dreaming of a dragon is a good sign, but dreaming of a black dragon means that you have been under a lot of pressure (including emotions) in your life and work recently, almost to the limit. I hope you can find out the reason carefully and adjust it in time.
In addition, someone recently upset you, made you angry and unhappy, so you dreamed of the black dragon, and even felt anxious and helpless in your dream. Beware of villains' schemes, and pay special attention to traffic safety when traveling.
I usually have this dream when I am in a bad mood or too tired, and I feel the same way. Don't take it to heart, be careful in everything and be patient with others.