(I don't know why I often dream about traveling around in complex train systems.)
I dreamed that I was on a train in the local train system in/around Copenhagen, with a couple old friends.
An area we were going to was nicknamed "Tivoli", according to the train station map. I did not know why, but I found out. (Tivoli is a venerable Copenhagen amusement park.)
Once out there, it happened that the train went into a tunnel, and then went downwards. Like 45 degrees downwards!
While hanging on for dear life, I asked my friends what the hell is this, and they said "have you never been in this area before?", and I said "apparently not by train!"
It went down like a roller coaster, except it went on and on and on and on, with gut-wrenching speed.
I thought, "how and when did Danish Rail have the time and money to build this??!"
It was absolutely, spectacularly terrifying. After I woke up, I had remnants of that fear for over an hour. (Yet it was not all that unpleasant, oddly.)
Then later it leveled out, and soon we came to a station. I ogled a beautiful woman getting off, and then we got off ourselves. I said that I knew the guy in the video store in this town, and we could do some kind of business with him.
When we went out of the station, the stars were out and the birds were singing. Even though the train had never turned upwards again, we were outdoors.
I thought about it a lot after waking, and I'm guessing I can learn that you can be afraid for no reason at all. And that even if it feels like you sometimes go down, there really are no levels.