I was 4ish years old when my parents took us up to Wisconsin to visit my grandma's family. We stayed at this hotel, I don't know the name of it, but it had an awesome pool. I always loved to swim so I spent most of the trip in the pool, playing with this other girl I met there. I don't remember what she looked like, but I remember having a friend at the pool who I would play and talk with, which was nice because my little brother was too small to swim and there weren't any other kids in the family we were visiting.
I had kind of forgotten about the hotel and the pool until years later. My grandma pulled me aside at her house and asked if I remembered the trip. I said yes, kind of, I was pretty young but I remembered the drive up and the pool. She said that I spent the whole time in the pool talking to an imaginary friend, laughing and playing like someone was really there with me.
That's not too weird, lots of little kids have imaginary friends, right? That's what she thought, too. As they checked out of the hotel my grandma mentioned how much her granddaughter loved the pool, that I'd made an imaginary friend there-another little girl my age, how cute it was--typical grandparent oohing and ahhing over a grandkid.
That's when hotel worker went pale and whispered to my grandma that a little girl around my age drowned in the pool the previous year.
She never mentioned it to my parents I guess, but that day she pulled me aside and told me the story I was shocked, because I do remember making a friend at the hotel pool.
ETA: I was kind of a weird kid and had a few experiences like this. I'll share later if there's any interest.