I only play this game when it's dark outside and/or I'm sleep deprived. The surreal atmosphere and aimless nature of the game beg you to get absorbed in it. You might start to drift off and think about something else, to make plans for tomorrow or reflect on the previous day. Yume Nikki is a strange, comfortable, uncomfortable walk in the subconscious mind of a person. For me, it pushed the boundaries for what I'd consider to be a "videogame" - I still remember back when "walking simulator" seemed to me like a valid insult to lob at videogames. But videogames aren't just Morrowind, or Dark Souls, or Tetris. They can be a lot of different things. Yume Nikki is the closest a videogame has ever gotten toward being a person, I feel.