This happened a couple of years ago in my old house when I was probably 13 or so. I'm 18 now. I was basically ridiculing the idea of demons of devils while I was in bed contemplating my day. I remember I asked myself, "If there ever was a demon, why don't they show up?" Sure enough, right as I said that, I felt a presence in my room. Although it was pitch black, I felt almost like a shadow move across my room until it floated over and around my body. I felt this frightening sensation in my heart/chest, like I was falling endlessly. I lost control of my conciousness, I could only percieve what this spirit like thing wanted to tell me: evil, consuming thoughts, maybe threats. It was this sense of insanity. I was deathly afraid of the spirit now. I remember talking to it through my mind, "Stop......stop......go away, I believe you." And as soon as I 'said that', the sensation stopped. I was only left with this eerie experience, and I could only comprehend it as being in the presence of an evil spirit. Its as if it wanted to prove to me that its kind does exist for some reason. To this day, I believe that demons do exist, but I've comforted myself that that must mean there is good spirits as well, maybe God. This may not sound that scary, but believe me, it was far too unreal at the time.