Two things worth telling right now in the same apartment, the rest can wait:
The first was when I was around 3 years old, young, but this was unforgettable, and for several nights in a row I had a repeated "nightmare" where I would argue with a dark presence under my bed who assumed the name of one of my friends and the"voice" of a character in one of my favorite kid's shows at the time. Then the darkness I couldn't see (in the town I was in my curtains really weren't that good in my bedroom so usually with natural human sight I could see the rest of my room, just not under there when that it was there at night) and I would wrestle and I would always be struggling to break free and it would try to pull me under my bunk bed (I was on the bottom bunk when I went to sleep but I would always wake up on the floor during this stretch despite never feeling any sort of fall). Eventually I would scream and I remember, clearer than yesterday, that as soon a my brother looked at me from the top bunk and my mother came down the hallway to check on me, the presence would disappear.
Thankfully, it didn't take long for my parent's to block the underneath of my bed with storage boxes full of clothes. After that, I had no more trouble with that darkness. Demonic if I've ever heard the word.
The second time was a lot less interesting. Basically, when I was 4 I was enjoying some fresh grapes after dinner with my brother. We talked, and eventually got into a playful argument. For some reason or game or another, he got up to run. I chased him for the same reason. Eventually I followed him to the bathroom where he locked himself in which I thought was unusual considering he is almost 3 years older than I am. Either way, I checked a couple times and I couldn't open the door, I yelled and told him he wasn't meant to do that (our parents above most disliked us playing with doors) but the only response I got was something along the lines of "you can't get me here" and then absolute silence even when I put my ear up to the door to listen for signs of life. So I quickly went back to the table to eat more grapes. As soon as I had turned around the corner to head towards the dining table, I saw my brother sitting there, almost done with the grapes. Neither he nor my mother remembered what I was talking about. Keep in mind the walls are all made of solid brick, and the door closed was very squeaky so it couldn't be opened behind my back without alerting me. After I went back, I checked the door again, it was unlocked and the bathroom empty. I was very confused. The chase was, from start to moment of realization, probably less than 20 seconds with half that being me staring at the locked door.
Pic rel is the layout of the chase.