I find your observation so completely accurate. I have a career that is all-consuming during my work week. I am able to think of my mom, whom I lost just over two years ago, with relatively little grief. I think of funny stories she told when I was a little girl, delicious Italian dinners, her immense beauty–and can actually feel joy.
On Sundays, however, I inevitably feel some degree of sadness. Perhaps some of that is that I lost Mom on a Sunday. I have come to accept this as my reality. I am still productive. I can still laugh. I can see tomorrow.
Not long after I lost Mom, I read something about grief that made complete sense–and that I have found to be absolutely accurate: Rather than fading with time, grief weaves itself into every aspect of our lives. It, then, does live alongside joy.