When I was 21 I lived in a tiny flat at the top of an old manor house (run down and in the loft).
After a while I started noticing weird things like some socks would be missing, or something would be out in the kitchen area that I just know I didn't leave out.
Gradually it got worse and ended up with things like the velux windows being open when I got in from work (I know I didnt do that because if it rained all my things would be ruined), once the bath was wet when I didn't have one that morning and had been at work all day.
I went to my mums for a week and my hot water switch was on when I got back, I had a coin meter which had barely any funds when I left so it would have run out the same day I left, but the water in the tap was hot when I got back!
When I slept in my bedroom (could fit a single bed with a tiny walk way to the door) I would leave the door open, I always had moon light in the frontroom/kitchen that I could see from my bed,
I should add that from my bed to the far corner of the living space was about 6 full paces.
One night something woke me up and when I opened my eyes I thought I could see a moonlit shadowy figure in the far corner, I closed my eyes and thought maybe I was still dreaming or something but when I opened them the figure was standing over me, like bent over and I could see little details in the dark like the shape of his nose and eyebrow. I closed my eyes again hoping to fuck I was still dreaming for some reason, then I heard the door click and it was gone.
It took me about 2 hours to get the balls to get out of bed in the dark, by this time the sun was coming up so I could see a bit more.
I had nowhere to go though and sort of doubted myself ..well I did doubt myself A LOT. I told the police but they didn't take me seriously, probably because I barely believed myself at the time.
I slept every night there with my mattress against the front door though since then. Moved out about 2 months later. It still gives me a panic when I think about now 10 years later! Creepy as fuck.