What I don't like is when I've had strongly emotional dreams and I wake up and the emotion is still there.
That can be pretty disturbing, depending on the intensity of the emotion.
When I graduated from grammar school back in 2001, I hadn't seen my first (and by the time ex) boyfriend in over a year. The break-up had been really nasty. During the graduation ceremony, the power went out for a while and we were all led outside. When the lights went back on, I thought I saw Henry (the ex) standing in the crowd.
When I told a classmate (who coincidentally was a friend of his I had been avoiding for this exact reason), she said that Henry had got sick half a year ago (lymphatic cancer), and that he was now in a coma.
Sure, I only thought I saw him because I had been thinking about him earlier (he switched schools a year before that), due to the end of an era feeling one gets at graduations....but I got seriously creeped out by the experience.
Two nights later, I dreamed of him for the first time in ages, and in the dream he said goodbye to me....next morning, that classmate of mine/ friend of his called me to tell me that he had passed on during the night.
Again, a coincidence, since I had just found out he was dying and was still trying to work up the courage to face his family at the hospital....but it was so horrible. I woke up crying, and an hour later that girl called me to give me the news.
So yeah....my "ghost encounter", if you will. There are logical reasons for what happened, but back then, it really got to me. That and the fact that he died before I could say goodbye.