You probably didn't need researchers at the University of Gothenburg in Sweden to tell you that Sunday is the most depressing day of the week. Few emotions are as instantly familiar as that deflating, edgy-yet-lethargic feeling seared into our psyches in childhood, and in Britain often accompanied by memories of bygone BBC programming: Songs Of Praise, Lovejoy, classic serials starring Imelda Staunton. Still, to rub it in, the Swedes analysed interviews with thousands of people – Germans, as it happens – so the folk wisdom about Sundays is now, in the language of media headlines, "official". There were nuances: married people experienced the Sunday mood-plunge more than the unmarried, and former west Germans felt it more than former east Germans (though they were gloomier to start with). But, overall, Sundays were saddest. And they don't have Songs Of Praise in Germany, so that can't be the reason.

At first glance, the real explanation seems unmysterious: it's the day before work or school restarts. These are the last hours of freedom, suffused with anticipation of unwilling toil. But there's more it: the modern Sunday, I think, is a lesson in how not to structure your life – or society – for maximum happiness.

The first hint that Sunday gloom isn't simply a rational response to returning to work comes from what happens when we actually get to work: numerous studies suggest we tend to enjoy the structure and goal-focus of our jobs. (The Labour Of Leisure, a new book by the sociologist Chris Rojek, argues that free time takes as much effort as "unfree" work.) But Sunday carries more meaning than "the day before work": it's meant to be (historically) an especially spiritually edifying day, or (nowadays) an especially relaxing, convivial one. And so it ignores two key rules of happiness. First, as soon as you label any period as "specially" enjoyable, you'll become so self-conscious, monitoring its specialness, that enjoyment is near-impossible. And second, in a culture that's no longer monoreligious, being told which day to set aside triggers an inevitable rebelliousness. I rarely want to go supermarket shopping on a Sunday evening until I remember it's forbidden. Add to all this Sunday's role as a temporal punctuation mark – "Reading the papers, drinking tea, ironing, a few more hours, and another week gone," as Jimmy Porter puts it in Look Back In Anger – and it's a bust. You couldn't invent a more dispiriting day if you tried.

Which explains why campaigns to "keep Sunday special" seem doomed, on their own terms, and leaving aside their Christian bias: you can't impose specialness. Perhaps we need strong laws to protect shopworkers' hours, but that's a separate matter. Meanwhile, stopping people doing what they want on Sunday won't automatically prompt them to do something more enjoyable, let alone more worthwhile. The Keep Sunday Special campaign doesn't even have the courage of its convictions: it lobbies to protect the current compromise, which creates neither a shopping-free nor frustration-free day.

Back in Germany, responding to a complaint from the churches, a court recently declared that relaxing Sunday trading laws would be unconstitutional on the grounds that Sundays should be for "spiritual elevation". Maybe they should; I'm no free-market extremist or hardcore atheist. But court-ordered spiritual elevation? Good luck with that.

oliver.burkeman@theguardian.com