Horror is like gravity. You can't really feel gravity unless you move in some way. Velocity is the same; we can't feel velocity in a car we're riding in until it changes. Horror is a transition from one moment to another moment with a perceptible change in risk. It's a state-change from a moment of low-level concern to a higher one. A good horror tale just keeps escalating, with one step-change after another.
That's what I'm trying to achieve in the third FLIGHTSUIT book.