I've told this story before, but about a decade ago I had banked enough PTO days that I was able to take off every Wednesday in the summer (with my boss's permission, natch). So I effectively worked no more than two days in a row for four straight months. Off weekends, work monday/tuesday, off Wednesday, then back to work Thursday/Friday.
The first month went about as expected - "yay! Wednesday off!!". But I wasn't expecting to experience what I did by the second month of my experiment: my mental health and attitude towards work had changed. That "Monday blues" you get was gone. Every work day felt like a "Thursday" or a "Friday" to me - because the "weekend" was no more than a day away. The dread of Sunday evenings knowing work was starting the following day disappeared.
By halfway through my experiment, I was happy to go to work because there was stuff I wanted to accomplish and thus was more efficient at my job. Nobody ever complained that I was gone every Wednesday for four months, my work always got finished on time (or ahead of schedule).
But I really was shocked at how my mental health improved by NOT working five days in a row.
I fully support a four day work week and wish everyone has the opportunity to experience what I did.