A few years ago I lived in an apartment with my mom, I was an only child and my parents had been divorced for some time. I had a habit of staying up late at night usually until 1AM. One night I wasn't to finish up a writing project I was working on. I went into my room at about 11PM and work on late into the night. In the middle of working my door suddenly opened, I looked at my clock noticing it was 3AM and called out, "I know mom I'll sleep soon."
With no response I looked at the door, it was cracked open, I walked over it peaking out into the hallway, seeing nothing I closed the door figuring it was the wind. Less then a minute after closing it the door opened again, I quickly closed it again figuring I hadn't shut it hard enough. The door opened a third time, at this point I was getting a little freaked so I ended up barricading the door.
After that everyone was pretty normal... Unless I happened to stay up until 3AM at which point the door would open almost exactly at 3AM. However if I were asleep at the time the door would be shut in the morning.
One day, I was in my room and at 3AM the door began to open... I looked at it not wanting to bother going to shut it. After another few minutes of working, I caught something out of the corner of my eyes, it was a quick movement and by the time I could move my head the door was being shut in the distance.
This freaked me out, I had thought that this was just some strange doorknob thing at 3AM but it seems that then it closes itself... Which means that the door could be opening without my knowledge every night.
I eventually started barricading the door before I slept. But even so in the morning every once and a while the chair would be slightly moved out of the way.