I don't remember it perfectly, so if it seems incoherent forgive me.
Me and my family had gone to an old house for some reason. You know the kind I mean, the old Victorian looking houses. Anyway, I think we were going to be staying there for a while. We were rather eager to explore the house, as it was rather sizeable. Old houses creep me out to begin with, but for some reason this one was especially foreboding. As I explored the house, I noticed pictures of the previous inhabitants, but they appeared to be old pictures, like same era as the house old. I then noticed that all the furniture seemed to be from the same era but really well preserved, almost perfect. I remember hearing something along the lines of "The house hasn't been lived in for nearly 100 years." At the time I thought it was just a line they were using to "sell" the house or attract tourists or something. As I explored, I began to feel more and more uneasy. As I rounded the corner the living room, I saw what appeared to be an old T.V., you know one of the old wooden cabinet style T.V.'s. I saw an image on the screen, thinking one of my family had turned it on I got closer. As I approached I knew something wasn't quite right. I got right in front of it and saw that it wasn't a T.V. at all but a tank, and inside, floating in a a greenish liquid, face pressed against the glass, was the perfectly preserved corpse of an old woman.
That was the only time I woke up genuinely terrified, it actually took me a good half an hour for me to realize it hadn't actually happened.
I was about 19 at the time, so it's not like I was a kid.
I don't know what it was, I mean I've seen stuff like that in movie's before, but in the dream I had very real sense of completely real completely unchained evil.
It was the only nightmare I remember in my 22 years of living.
I still get scared thinking about it.