Here's one of my nightmares...

I'm on a train, I don't know why because it's not the kind of train I've ever seen except on films.

It's poorly constructed and made of weathered old wooden boards and there are massive open doors on either side of the carriage and a trap door in the roof.
Not the kind with seats for passengers, the kind people stow away on that never seem to contain anything as they run through empty country for days on end.

I know, because I know I've been here before and I know what's coming which is making me shake, even though it seems so ordinary to know that there is a creature on the train, bipedal and fierce with fangs and claws and hateful hungry eyes and I know it's coming and all it wants is to tear into me.

I run to one door and I try to close it, but the door is too big and I only just manage to force it closed before I hear this thing land on the roof, but the other door is open, a massive gaping hole in the side of the box that I know can't protect me even as I run over and tug at the rusty old handle to try and close it, wondering why I'm bothering when there is a door in the roof and none of them have locks anyway but I can't help myself, I run from one door to another trying to keep them closed while it plays with me because I am prey, tugging at one door, then bounding across the roof to tug at the other, scenting me working up a frightened sweat until I can hardly get a grip on the handles because I'm just running with sweat.

After forever and a half it starts to tear through the walls and I've got nowhere left to run.
I turn away, I never see it clearly even though there's daylight pouring through gaping holes it's torn through the woodworm ridden boards and I catch my foot on something and I fall.

It bites off my foot, but I try to crawl away anyway and it takes the other leg up to the knee.
I keep crawling away while I can hear it ripping through what used to be a part of me, then it comes back for what's left of both legs and all of me up to my ribcage but I'm still crawling along and away feeling those bits tear away as I try to escape with mess trailing out from beneath my ribcage which is the only part of my body touching the floor apart from my elbows and I'm screaming because it hurts so very much and I know you can't survive this, that I shouldn't even be alive and then I turn around and I tear out it's throat with my own teeth.

That's when I start to scream because I'm enjoying hurting it.

That's when I wake up and find I'm still screaming.