A body can be entirely safe and not feel it. Anyone who has spent the last day of a holiday dreading the Monday knows the arrangement: sun, no obligations, nothing whatever wrong, and a nervous system filing reports from a different week.
Which suggests the feeling isn't downstream of the facts in the way you'd expect. It runs on anticipation, and anticipation can be pointed in either direction on roughly equal evidence.
Permission is the operative part, and it tends to be withheld until some future condition is met — the money, the results, the thing on Friday. Given that those conditions keep moving, it may as well be granted early. It costs nothing, and the week runs better on it.