The film that most upset, that is, rather than scare, made me so uneasy that my stomach was tied in knots, though I had already seen it once, was not a horror film as we know it. It was SPARROWS; I have been terrified of quicksand since childhood, & this film was full of it. Not only Q, but kids trying to escape this evil slave driver through a swamp filled with alligators, snakes, and Quicksand.
Though having already seen it once, I was so uneasy, I simply could not continue it. When I 1st watched it, I had taped it months ago, but was too apprehensive about it, so it just sat there for I cannot remember how long.
It may have been a Tarzan film that first made me aware that the ground itself could swallow me, as recently TCM has been running just about every Tarzan film, & no fewer than four had Q in them. Two of them relieved Tarzan of the necessity of killing the villains via them stepping into it, no, three at least. Several film versions of THE HOUND OF THE BASKERVILLES show people at least foundering in Q, & there was a PBS show shown in elementary school that ended with a boy BOG HOPPING, but not quite leaping far enough. I believe this program was intended to inspire us to read the books. The guy who told the story made several sketches to help intrigue the kids into borrowing these book, etc, & the last one terrified me.
I had nightmares about be swallowed by quicksand, even being CHASED by quicksand.

Other that helplessness in general, this scares me more than anything else.