When I have been sitting for 1 hour, I sometimes notice that my legs are stiff and I feel dizzy. I do drink lots of water and herbal tea throughout the day.

This can be due to the gradual drop in blood pressure that can be caused by a lack of movement. The stiffness can also occur when weak blood flow starts to reduce the delivery of oxygen and nutrients around the body. There's no option but to move more! Flex your legs whilst sitting; do arm exercises in between emails; focus on good posture (to avoid cramping the lungs) and full breaths. And jump about as much as possible in between the inactive phases. You may also like to check your iron levels with your doctor, as even mild anaemia can make dizziness more likely.