One time when I was a kid I was playing hide and seek with a family friend that would watch me while my parents were at work. I was hiding behind a couch downstairs when I heard her shout that she'd found me and was going to go back to watching tv. At first I thought she was messing with me so I stayed hidden for a while but after a half hour I realized that she wasn't looking for me so I went to go ask what happened. She was insistent that she'd found me. She said that she was going up the stairs and when she looked up she saw me run by. I hadn't been upstairs.
Around that same time I got a fancy new camera and spent the whole first roll of film just taking a million pictures of anything I could. When we got the film developed I came across one particular picture I took of three of our cats. I remembered seeing the three cats lined up in perfect symmetry on the stairs and how excited I was that I was able to get a picture of it before one of them moved and fucked it all up. The picture was shot from the side of the stairs, and in the picture you can clearly see my smiling face peeking down from the top step and staring straight into the camera. Except I was the one who took the fucking picture. My parents tried to play it off and claim that they took the picture but then it went missing. When I asked if they'd thrown it away they pretended to have no idea what I was talking about.
Fast forward to when I was 19-20. I was out with friends one night when I got a panicked call from my parents. They were furious with me. They immediately started asking if I was on drugs and going on about how I'm too old for phone pranks. I had no idea what they were talking about. They said that I kept calling them and asking them to come up to my bedroom to help me because I was sick. They said it sounded like I was in a world of pain but that it was definitely my voice, and the calls came from my number. When they went to my room they didn't see anything out of the ordinary.
A lot of weird shit happened in that house in general over the years but the doppleganger thing is the one that creeps me out the most. I'm sure there is a rational explanation out there somewhere and they were all probably just a series of coincidences and overactive imaginations but I still wonder sometimes.