In my old apartment, my dog would, on occasion, look down the hallway towards the bedroom, from the living room, and growl, for no apparent reason. Also on occasion, when I was sleeping in the bedroom (she slept at the foot of the bed), I would wake up with her staring intently at the door and growling. She was a big girl - 140 pounds of Great Dane, Catahoula, and slobber.
So I'm there for a couple of years of this, thinking, ok, my dog has a good imagination.
Wrong. One night I woke up due not to my dog growling, but barking for all she was worth. And not at the door... she was barking straight at me. I opened my eyes pretty much immediately, and there was a blur of light, leaning over me, very close - certainly less than six inches from my face. It was not distinguishable as a person - it more resembled a person-sized version of a colorful nebula you might see a picture of in a science magazine. Three dimensional and all. I immediately got the distinct impression that this thing had been watching me sleep. For god knows how long, and how many times before. For all the clarity of that distinct feeling, I had no sense of what it wanted, whether it was malevolent or just curious. I flipped right the fuck out - jumped backwards to the other side of the bed, too terrified to scream, and that blur of light receded and disappeared over the course of about 3 seconds. My dog was going absolutely ape.
So, shortly thereafter, I asked the building manager if anybody had ever died there. She investigated that, and came back to me a couple of weeks later with a yes, a woman had died of a drug overdose in that apartment in 1995 (so 12 years earlier), shortly after having her child removed from her custody because of her addiction problems.
My dog did still growl at the hallway from time to time, but I never saw it again. I moved out about a year later.
I've had other encounters, but this thing was literally inches from my face, watching me sleep. Getting shivers now just writing about it.