What does my dream/nightmare mean?

I just had a dream/nightmare of this random older man, who I don't know at all, drive behind me on this road and when we got up to some railroad tracks the arms were coming down and he didn't stop. He drove around me and then proceeded to stop on the railroad tracks while a train was coming. I yelled at him to get out of his car and he refused and told me something like he had lived his life or it was his time. The next thing I remember is the train hitting the car, killing him, and seeing his decapitated head land near my car. I'm completely freaked out. Does anyone know what this dream/nightmare might mean?