When I was a kid, I used to have dreams about tornadoes. The worst one was about a tornado at my grandparents house, it was literally chasing me around the house. Keep in mind I was maybe 7 or 8 then lol!
My worst adult dream was very creepy, and was a true wake-up call. I had it many years ago, prob. in my mid to late twenties. I was in this house, and a well dressed, very official, no-nonsense kind of man said he has something he wanted to show me. So we went down, way down into what appeared to be a basement, like a laboratory you might see in an old movie. There was a terribly undescribable stench in this place, it was horrible. There was a man seated in a chair, I think he was naked. and there were tubes hooked up to him. I asked my "guide" what was going on, he said something about transferring his blood. I asked why, no response. I looked around and told my "guide" that I've seen enough, as I felt like I was in Hell. He said "I'm sorry, you can't leave." At this point I got very rebellious and determined, and said Oh yes I am! And somehow I willed myself up through the depths, and woke up scared out of my wits, and very thankful to be at home, in my bed still alive. I had a different outlook after this. Don't think I've ever been so scared.