Aye, Environment is key to scaring the crap out of yourself.
I still say the Langoliers is the scariest movie of all. I saw it like three times when I was like 5-8 and I always had nightmares about the floor of my house and the ground falling away into nothingness. Trust me, there the worst dreams. I felt completely terrified when I had these dreams and sometimes I had dreams were the Langoliers would eat my friends and family. If you watch the movie in the right environment its bound to give you nightmares.