I had one in like...4th or 5th grade where I was in this roundish room, with red walls or bricks and a big window at the end. I was back in the opposite corner of the room scared for my life as this black ooze or whatever was floating back and forth around in like in Anime whatnot. There were also glass cases with things in them and I couldn't see in them. Scared the **** outta me and I woke up. Last summer in early June, I was visiting the Smithsonian Institute I turned around and broke into a cold sweat. Was weird.

Here's the room: