I am not a religious person, more scientifically orientated, but must remain open to possibilities, since I too have experienced something that has by now deeply rattled me and after searching online for explanations (never a satisfactory one) I have decided to share my experiences and see if anyone can offer any input.
It first happened around 8-9 years ago, but I didn't quite want to take it seriously. It always happens late at night, perhaps sometime in the very early morning. I've always been a very light sleeper and usually go to bed late (more of a night owl). So I was laying in my bed, trying to fall asleep and once I reached that plateau, just before falling asleep but not quite, I got disturbed by a Very uneasy and horrible feeling of someone standing at the door to my room and staring at me intently. It felt like pure and utter evil watching me. I don't frighten easily at all, but then and there fear took control over me in a way that I wasn't accustomed to (lack of control probably increased it). In short, the feeling was nothing like I'd ever experienced before. I tried to rationalize and calm myself down and kept saying "it's all in your head, you're sleep deprived, it's nonsense, don't be stupid", but all the while I felt like this 'presence' was very slowly, but gloatingly moving closer and closer to me, as if trying to get into me. I started chanting the same words with more focus, rationalizing and rebelling to the fear that this thing tried to instill in me and then it disappeared. In the morning, although I was quite disturbed, I just dismissed it as a bad dream and went on with my life until the next time it happened and it didn't happen to just me.
My friends came over one night and we had a small party, sure some drinking was involved, but not drastically. One of my friends decided to sleep over, to avoid driving that late. We both fell asleep in my living room, her at one side and me on the other side, and then I had the same exact feelings of some purely evil entity standing at the door and watching us both. The same fear-inducing, gloating malice like the first time. Again I struggled to keep control over myself in the darkness and decided I'll just ignore it and slap the 'entity' in the face by turning around and going to sleep. It seemed to have worked, however when I woke in the morning my friend looked quite disturbed and we both just mentioned that we had an awful night and then she said she's never going to sleep over at my place because she felt so afraid at night. She said she was afraid to fall asleep because she believed something enraged and evil was watching us. When she said that I was in complete shock. If it was a bad dream, can two people really share one? Or did we both really experience something what I up to that point thought was unfathomable. I told her I experienced the exact same thing and to this day, she doesn't want to stay over at my place because she believes it's being haunted by something. I however became more intrigued by these strange occurrences and obviously tried to search info online. I found that sleep paralysis may produce similar sensations to what we've experienced, but the thing is, I was never paralyzed, I could move freely.
Anyway, a few of such experiences occurred a few more times over the years, and then I moved abroad for 5 years, never experiencing anything like that until I came back home to my flat this year. The first night I slept in my bed this year was unusual and almost evolved. I was laying turned towards the wall, trying to sleep on my side, I left the door to my room open (it leads to my living room). Then it started again, slightly different this time. First it was just pure feeling that there is someone there in my living room, a presence, but it didn't feel evil... I have wooden floors everywhere and then I suddenly heard what I thought was a dog trotting across the living room towards my room (claws hitting off the wooden floor with each stride) as if it was running in front of something, or I felt as if its running towards me to warn me or protect me. I didn't dare turn around, I just hoped that if I ignore it all, it will just go away. But no, what totally freaked me out was that the trot didn't stop, the 'dog-entity' ran all the way to my bed then jumped and something landed right by my feed on my bed. It really felt like a dog had jumped onto my bed. My dog, who passed away, used to sleep at my feet, but he was massive, he couldn't really jump on (always needed to push him up) as he was fat and lazy, but this felt more like an energetic light pup. It felt almost as if it ran to me for cover or warning. And then the real deal started. Again I felt that evil presence approaching me but this time faster and with this anger/rage coming from it. I didn't want to move so I stayed on my side, back turned against the entity. My hairs stood up at my neck, got the goose-bumps and very eerie feeling as if the entity was literally breathing down the back of my neck and trying to elicit a fearful response from me or something... I don't know what it wanted, I just know it felt like it wanted something from me. I could barely hold myself together not to show my panic, so again I decided to play cool and phlegmatic and I shook my shoulder and waved with my hand in a shooing motion and said "go away, enough" out loud. And it did... It felt like some bitter victory in a weird power-struggle.
The last such event happened less than a week ago. Again, late at night, me turned towards the wall, casually trying to fall asleep and all of the sudden, the thing was there again, I didn't see it, I could only feel it, very strongly. I refused to turn around and opted for the usual tactic of ignoring and dismissing. This time I felt it was stronger and much angrier than before. It got really close to me, again as if breathing down the back of my neck and as if applying a very strong mental focus or intention onto my head. It felt as if it was trying really really hard to get inside my head, so much so that this time I heard a very unusual sort of buzzing (like a swarm of bees but more mechanical/electric, like mixed with a Tesla coil sound), as if some static charge or something like that was being emitted around the back of my neck and head. A very unpleasant and unusual experience. This was by far the worst of them all. This was the first time I physically felt something was trying to manipulate me, get inside of me. This time I decided to react and not ignore, so I swiftly and angrily sat up and turned on the light. But there was nothing there, absolutely nothing... It left me sleepless for nights, I was never afraid of the dark, but this time, these experiences have started to freak me out a bit, because I wish I could find out what all of this was and what it wants from me.