It's not an entire movie which gave me nightmares as a child -- it's a moment from a movie. I went through enough real horror as a young girl, not to seek out the make-believe kind, so I never watched scary movies. One day I was alone at home trying to find something to watch on TV. As I switched from channel to channel, I suddenly came across a scene from some old black and white horror film: A child was peacefully sleeping in a darkened room, the camera slowly pans over to the closet, the door is ajar... and the Wolfman (or some such creature) is watching him! ...Well, let me tell you, for years after that before I could go to sleep I had to check to make sure the closet door was firmly closed - and of course that the Wolfman was not inside.
The other film which, as an adult, just touched some weird place inside me was CRIES AND WHISPERS. Don't ask me why, I don't know. Even thought the title suggests it, it's no horror film. But as I was sitting in the theater watching it, very involved, my heart suddenly started to beat so fast I thought it would burst right through my chest and i could hardly breathe. I tried to calm down, but couldn't and finally had to leave.