Having a good stretch once or twice a day feels good and can help prevent injuries (flexible muscles can do more), improve your posture (and as a result help with back pain), increase blood and nutrients to your muscles, and help you to feel less stressed.
Lie on your back, bring your knee to your chest and then across your body. So your right knee will go over to the left side of your body. Hold this for at least 30 seconds. Then stretch the other side.
Sit with your legs straight out in front of you stretch your arms up to the sky and then bend forward as far as you can.
Other quick stretches (you can do these at your desk)
Clasp your hands behind you and pull back to stretch your chest.
Hold your arm in front of your body and stretch it into your chest.
Stretch your neck from side to side or do neck rolls.
I bet you are feeling better already!