Disclaimer: I don't really believe in this sort of stuff but I have no other explanation than a really creepy coincidence.
When I was 14 years old I lived in an apartment with my family. Over time, in this apartment, we had 3 cats and 1 dog. All at different times. All of them, even though they never knew about each others existence, had this one corner in our living room that they hated. The dog occasionally stood there, looking and barking with his fur up at the corner between the ceiling and the 2 walls. The cats had the same thing. They stood there, looking up with their back arched and their fur raised and making that hostile sound cats make when they are about to attack something. Now while this is creepy as is, I had to sleep in the room that is connected to that se living room with a fully transparent sliding glass door. As a 14 year old kid, I really liked reading about supernatural things and witchcraft and that kind of stuff. One day, I surfed the website of someone who calls himself Puzuzu, and the entrance to the website was this blue Pentagram on a black background with demons dancing on and around it. When I went to sleep, my screen was already in sleep mode and apparently this site was on in the browser. For those of you who remember the old, bulky screens, they used to make a little "tick" sound when they powered up from sleep mode.
So I remember having a horrible nightmare. This was one of the only times I actuay woke up jumping to sitting position, covered in cold sweat. The moment I woke up from the nightmare, I heard this "tick" sound of my monitor powering up, and what I see in the screen is this blue pentagram with demons dancing around it.
I fucking froze for like 5 minutes before I could get myself to move and close it.
And this is the creepyest thing that ever happened to me. Thanks for reading!
TL;DR: had different cats and dogs barking/hissing at the same corner i the house, woke up from a nightmare, monitor turned on by itself and saw big ass pentagram with demons dancing around it, my aoul shat itself and I froze out of fear because it was creepy af.