Well, I don't have one single worst. I often have nightmares. A few really horrifying ones though are the following two, both of which I have dreamt twice, with a slight variation in the rerun. Bear in mind that both nightmares, or all four, if you will, were dreamt by me somewhere between being eight and twelve years old. So they were happening to a little boy.
Number one: (I dreamt this one in two versions, mainly different in that in the second one, the floor and walls of the room where I start are invisible, and the vampire pirates can see me instantly) Alright, so I'll tell the first version of this dream, having already explained the difference in the second. The nightmare starts with me standing in the upstairs bathroom in the house that belonged to my, at that time, best friend's parents. I started sneaking out of the bathroom and down the stairs to the ground floor, and as I sneak along I can hear someone pillaging the house. As I get downstairs and start making for the door, they spot me, and I spot them. They turn out to be vampire pirates. They chase me from the house. Instantly after escaping the house I find myself in the local park. But where there used to be a football field there now is a rotting, festering swamp. In the middle of it there is a derelict pirate ship teeming with vampire pirates. Once again I am chased from the scene, and I run for my home. On the way I meet my older brother, who escorts me on the way home while I tell him what has happened. He tells me not to worry as I am with him now, and that he can spot vampires from miles away. Just as he says so, two beuatiful women come walking the other way, right in front of us, and in the passing they snarl, showing their teeth, revealing themselves to be vampires, without my brother noticing.
Another horrible nightmare, also uncluding vampires, goes thusly:
I find myself at a party, and there is a knock at the door. Everyone tells me not to open the door, and I cannot see anyone out there through the blurred glass door. I do open the door however, and as I do a menacingly evil laughter fills the vicinity, I look down and see footprints being made as someone invisible enters the house. Suddenly everyone starts screaming as half the party attendants have turned into vampires, as it would turn out, I let Dracula himself in. The other half of us flees into the cellar and wait there for our inevitable doom. We stand in the cellar while we can hear the vampires frolicking about upstairs. I see that further into the cellar there is a bathroom. I go in and hide in there. Only problem is that once inside, I can see through the walls, and I am left to wonder wether this also applies to people on the other side.
This dream was returned at a later time, only this time it ended witht he vampires spilling into the cellar after I had hidden in the bathroom. It turns out that they could see through the walls aswell.
I might return with more if I remember any other nightmares.