I think it may have been shared. In fact, one Lucid dream I went down the stairs in my house and there was this girl there who seemed very real. Some how I knew she was not a dream person, or a dreamer. I think she was a spirit and I took her into the kitchen and asked her some questions. I told her that I was not in spirit mode but in dream mode. When she heard this she seemed wary and worried. I asked her what would happen if anyone found out and she said "they will try to make your life end shorter than it should." To which I said "I see" meanwhile thinking that she just confirmed my worst fears. Now, could she have been talking about assassins like the one in your dream?