informal if you have that Monday morning feeling, you are unhappy that the weekend has finished and you have to go back to work.
'You look fed up. What's wrong?' 'Oh, it's just that Monday morning feeling.'
that Monday morning feeling
The listlessness and dissatisfaction felt upon returning to work on Monday after the weekend. Ugh, I'm getting that Monday morning feeling already and it's still Sunday night! I don't want the weekend to end.
that Monday ˈmorning feeling
a feeling of being depressed because you have to start a new week back at work: In my new job, I never have that awful Monday morning feeling.