Ok so before I say the name I want to explain the story. I was 6 or 7 when my aunt and her friends brought it home and they were insistent I could not watch this movie but I snuck into the living room and eventually sat with my aunt. It took 1 scene to send me into such a panic I to this day can't sleep for days after I willingly watch it. This movie warped my sense of horror and not a single movie has lived up to it. The movie is the exorcist from 1973 and the 1 scene was the bedroom scene where the bed starts moving and her body begins to change.
When I was 7, I caught a glimpse of this movie from the top of the stairs as my parents watched it in the living room below. It just happened to be the scene when she first twists her head around. It was the only time I've ever been paralyzed by fear and could only run to my room after the shock had passed.