Why does it feel so good to stretch? Because it's a form of movement that both energizes and relaxes at the same time. Stretching requires deeper breathing, which sends oxygen and energy through your body. It simultaneously releases tension stored in your muscles.
Try taking a stretching break when you're feeling stressed or tired. It's as easy as reaching for the ceiling while you're sitting or standing, wiggling your fingers as you hold the stretch for 10 to 20 seconds or so. Then stand up and reach one arm over your head as you tilt from the waist in the same direction. Finally, reach down toward your toes. (It doesn't matter if you can't stretch quite that far. As one wag said, "If God meant for us to touch our toes, he would have put them on our knees.") Don't forget to breathe slowly and deeply throughout.