This is the same impression I got, precisely because of this description. If it's the effect of a field, it would seem that by the point you notice it blocking your forward progress, you're already rather deep in it.

Perhaps humans feel resistance/repulsive forces non-linearly?

Makes me think of magnets, too - when you have two strong magnets oriented so they repel each other, and try to get them closer, the effect is very strongly non-linear and, unless you're intentionally pushing the magnets together with significant force, can feel like it turns on almost instantly.