Similar to consuming lots of sugar and caffeine, the more stressed out you get, the less time you make for exercise.  The less active you become, the more stressed out you become.  If you can get your heart rate up, even for 10 minutes, you allow your brain to reset itself, and your stress level will immediately decrease. You can add motion to almost anything you do.  Try walking in place or pace back and forth while on the phone or do a couple sets of crunches or lunges while watching television.  If you are really ambitious, you can download a yoga or meditation video – which focuses on helping you relax, and often is as short as 10 minutes.