When my brother was little, he used to have an imaginary friend that he would play with. My parents didn't really think much of it until one day they realized that he hadn't talked or played with his imaginary friend for awhile so they asked him about him and he said that they weren't friends anymore and refused to say any more about it. My parents left it alone figuring he'd probably just grown out of it and that was his way of saying it. Not long after, my brother would get terrible night terrors. Something about the man in the black hat was coming to hurt him and me (I was really little at the time. My brother is older than me). My brother had described his imaginary friend as a man in a black hat. A few months after this started, my brother started getting terrible migraines. My dad's brother died of brain cancer at age 5 so my dad didn't want to take any risks with my brother and started bringing him to the doctor. He got all sorts of MRI's and CT scans and stuff but everything was normal and he eventually stopped getting both night terrors and migraines and nothing bad ever happened to me.
Fast forward a few years, we got a dog. My dog would frequently stand at the top of the stairs looking into my room, hackles raised and growling menacingly at apparently nothing. My mom distinctly remembers this happening on several occasions. It was around the same time appliances in our house would randomly turn on and off. The toilet would flush, the microwave would turn on, the radio wouldn't turn off, etc. It was also around this time that I developed sleeping problems that I've had ever since I was little. I don't remember this since I was still pretty little but my parents told me that I would wake up in the middle of the night and they would hear me crying so they would come to check on me and I would tell them there were people in my room. There was no one there. It got so bad an so frequent that my dad would sleep outside my bedroom in case there was someone coming into the house at night. The nights that he did that, I never woke up, but the dog would start barking in the middle of the night so he would check out the windows and check on the dog and never saw anyone outside or anything. Eventually, this stopped too and everything went back to normal again.
Fast forward again to my pre-teen years and my friend got a ouija board. We played around on it and decided to ask it if there was a ghost in my house. It said there was and his name was Christopher. We did the typical ask how he died and how old he was and what did he look like, etc. He was an older man and had died at home. He liked to wear a black hat. I hadn't told any of my friends about my brother's imaginary friend so that really freaked me out and I told my friend to take her ouija board out of my house and not bring it back ever. I later asked my parents about the man in the black hat and they also got pretty freaked out. Once again, the dog would bark at night and growl at nothing. I had nightmares for about a month straight after that but eventually everything went back to normal again.
Fast forward to shortly after I graduated high school. My parents had gone away on a trip to Peru and my brother had long since moved away from home. I was home with the dog for about 2 months by myself and my insomnia got really bad. I averaged about two hours of sleep per night for most of the time my parents were away. I started seeing things out of the corners of my eyes like little shadows that weren't there and what looked like demons or imps or something hiding in dark corners. I let my dog sleep in my room with me at night because it was freaking me out. Several times, my dog would wake up and stand at my door, hackles up, snarling at the door. I was too afraid to ever go and look on the other side of the door, but eventually, my dog would calm down and lie down again as though nothing had happened.
A few days before my parents got home, I was in the kitchen and noticed my dog was standing in the hallway looking like she was ready to attack something. She was snarling pretty ferociously so I picked up a big knife and walked into the hallway to see what was going on. There, standing at the end of the hallway, clear as I could see my dog, was an old man in a black top hat. I ran back into the kitchen, picked up the phone and called my best friend to come over. I went back into the hallway and the man was gone. My dog was calm as well so I put the knife away and hung out with my friend for awhile. When my parents got back, I started sleeping more normal hours and stopped having hallucinations. Nothing really strange has happened since then, but that was probably the creepiest thing I've ever experienced.