Even though its a bit dated... and it doesn't scare me (well there are parts)... I think I have some PTSD from it. Now I was probably 9 or 10 when I saw it on TV. And there were rumors (or news, not sure) of people having heart attacks at the theater. So, I think I must have justified my fear from believing others thought it was the scariest movie ever. It was literally weeks before I could sleep alone and even more when I didn't feel my bed shaking. And then I was sure "it" was under my bed, so I stopped walking near it. So to say it traumatized me I think is probably pretty accurate. So even today the mere mention of it brings up something... and I don't watch it when it is on.
For whatever reason there was a book from Jay Ansen called 666 in our house. To this day I have no idea why because no one in our house would have read it or anything like it.... We barely had a Beatles album, lol Its possible it was left by relatives or friends or something. I guess I was 12 or so when I read it. I believe it was the same author that wrote the Amityville Horror. Which I am pretty sure I saw, and was scared by, by then. But I remember being frightened reading the book... I doubt I could have read the Exorcist and I don't think I would want to anyway.