When we are concentrating on a task or reading for a period of time, we often assume a slouched position which can restrict the capacity of the chest to expand with a full breath. And when we are tense, part of the stress response is that breathing becomes shallower.
Taking a minute to breathe can lift the energy, calm the mind and make you feel more centred.
Try these exercises one at a time, breathing through the nose and making each breath as deep and full as you can. Continue for as long as you like, closing your eyes and focussing inwards once you have established the breathing pattern. Notice any changes in how you feel and whether the different practices produce different effects for you.