Deep sleep comes difficult to those who are shallow breathers as the sympathetic nervous system of theirs is active which raises the heart-rate. To avoid this, you need to lie on your back and practice surrendered breathing where you wait for the breaths to come and get our mind out of the way. When you're trying to breath, there's tension in your body and so your rib cage is tense and can't expand it right. Surrendered breathing helps in relaxing your body completely which creates much space in your body to breathe.
by Dhwani Vora