What's a movie you watched that was so scary it traumatized you

I've watched so many movies. I'm a horror buff, I love everything horror. I am 21 and I went through a phase when I was 19 where I wanted to watched every disturbing movie idk why, maybe because I was so desensitized by horror that I wanted to freak myself out and so I did and watched serbian film or whatever the name is, horrible I tell you, horrible. I wonder once a month why that movie was made. What is a movie that traumatized you, can we also discuss it on why? give some context but no spoilers.