I'm not someone who is afraid of the dark, and even use it as my "element" along with Water/Ice. But the way these games work is that they do make you afraid. They make you feel powerless and need to struggle to survive against something you can't touch or defend against without light. It may have to do with how atmospheric they are as well. They really immerse you, and when you play with only the lamp on making for little light in the room, alone with your headphones. And configure the in-game settings so that it looks dark to you. It immerses you very well which is the best way to play the games.
Problem with Amnesia however is that the scary events & enemies are scripted. So after experiencing them once, it isn't as scary when you replay the game and learn the mechanics behind how the game's event triggers are setup. It's scary the 1st time around, but will be very hard to capture the same feeling on future playthroughs. It's still a very intense and fun experience despite this.