[Stingy Jack]

I completely agree with Vod about the "Hopelessness" element. I think this is the main reason why The Texas Chainsaw Massacre is so great. No movie does hopelessness better than this.

The only element in the list that frightens me is "fear of the unknown". The monsters (or whatever frightening thing it is) in a film are always scarier when you don't see it. But, as soon as you see it, you can deal with it right away (and it never lives up to your expectations.)

The claustrophobia element is good ... but I think that goes hand-in-hand with hopelessness.

I was also going to add "oppressiveness" and "relentlessness", but those go right along with hopelessness too.