Are Amnesia players adults or teens?

[Bridge]

Dude, who said that I was talking about you?

And how can a game give you nightmares? I mean.. Am I really the only one who never had problems with any horror movie or game?

It's possible you don't want to be scared and therefore don't let yourself. If you think that makes you cool, then you should know that almost everyone here agrees that not being scared is a missed opportunity, as well as usually being the player's fault. Unless waking up in a strange castle with no memory of who you are and having to evade monsters is a normal thing for you, I don't see how you can not be scared - because it is scary.

I was not talking about being scared, I was talking about nightmares man

Even so, it is not that surprising. After only 30 seconds of looking at an image your brain stores a very vivid copy of that same image that you can peruse for around 5-10 minutes. Now imagine looking at a collection of horrifying images, coupled with feelings of intense emotional stress for hours right before bed. Those images are going to be literally burned into your inner eye the entire night. Since the brain is designed to remember things that are threatening, seeing those images constantly reminds the brain of what you felt when you saw them. Ergo, the game continues even after you stop playing it. It doesn't really matter if you have an actual nightmare, not being able to sleep due to fear is a metaphorical nightmare in and of itself.