If you have to sit all day long, whether you notice or not, your hip flexors probably get really tight. Now and again they could probably do with a little stretch. Try this stretch to ease your hip flexors and give you a break from paperwork.
Get down on your knees (ideally on a carpeted surface). Then bring one leg up so that you are on one knee and one foot (as if you were proposing). Inch your front leg (the one with the foot on the ground) forward so that you have room to bend (from the knee) forward into that leg. Make sure you keep your front knee behind your toes when you bend forward. That will protect your knee. You should be able to tap the ball of your foot, not just the toes. If you can’t, you might want to move your foot forward more. Hold that stretch. You should feel it through the front of your back leg. And it should feel glorious (or at least pretty good). Repeat on the other side.