When I was around 13 years old I was lying awake in bed, my sister asleep in the same room. I was restless and feeling increasingly convinced someone or something was watching me. As I squinted my eyes in the darkness I could make out a shape similar to a man standing at the foot of my bed. There were no facial features, he didn't seem to be wearing any clothes or headgear, but there was a definite "blackness" or void that stuck out in the blackness of the room. This creature was blacker than the night; his structure was denser than the darkness of the room. I don't know whether it was because I was a teenager and hadn't experienced anything like this before, or because this thing was in fact a menacing creature of the night, but I felt completely terrified. I wanted to scream, to awake my parents and my sister, but thought this thing may harm them if I woke them. So I closed my eyes tight and lay there, trying not to breathe, my heartbeat seemed so loud in my head.
Well I don't know whether it annoyed the shadow person but then "he" began moving the bottom of my mattress up and down repeatedly. I guess either he wanted to get my attention or wanted to terrify me to death! Perhaps he wanted to feed off my fear?
Well I wasn't in the mood to have a conversation with him so I lay there as silent as I could and eventually, after what seemed an eternity, he must have gotten the hint and left me alone.
I know he was real because I hadn't been asleep before his appearance. But now I'm older I wonder ~ I guess it's like what came first, the chicken or the egg? Did I really sense that there was something dark at the bottom of the bed? Perhaps my own made up fears, added to the complex nature of a growing/hormonal teenage girl manifested that creature from my own manmade fears? If I hadn't manifested it, but it was a real living creature from, say, another dimension, was it actually menacing or desperate to communicate?
I think even a grown adult (even one who was into ghost hunting or, um, martial arts, lol) would be at least a little un-nerved by the presence of some dark matter that did not have any facial expressions or talk.