Oxygen is one of the inputs into the chemical reaction that creates energy in our cells ... and yet so few of us ever actually think about how we breathe. Mainly because we don't have to - it happens automatically - but poor posture, stress and habit means that most of us fill less than half our lungs with each breath.
I find the exercise below is useful to get in the habit of deep breathing, oxygenate the body and provide a pre-bed relaxation for restful sleep. However it's also a good idea to take a few deep breaths whenever you're feeling tired or stressed.
Sit in a comfortable position on the floor or a chair - with a straight back. You may find it helpful to sit with your back against the wall to support a weak back.
Close your eyes and take a deep breath in filling your lungs which should bring your chest up and your belly out. Count as you breath in and then take the same number of counts to breath out. Repeat for 30 breaths and as you breath try and keep your mind still and focus just on how the breath sounds and feels. Over the 30 breaths your breathing should slow and your mind become quiet. When you've finished open your eyes and enjoy the feeling of relaxation you've induced. Enjoy!