Hard to put this succinctly but it has a sense of the sad and exhausted feeling one gets when they're mildly sick and must stay home, and likely stay in bed, to recover but you don't really want to do so.

In other words, Sunday is our only true day to rest, the weekday was busy with work and scattered after-work commitments, and Saturday was devoted to a combination of chores and using every last bit of energy you had in the week to enjoy life and friends. So we may try to mentally force ourselves to take a day of rest and limited exertion, which in turn makes it not restful or fulfilling.

It's sort of like when you know you need to go to bed on time so that you can have full energy for a busy tomorrow, it somehow makes your sleep worse knowing that.