Sometimes how we position our physical body is key to how we can find our natural breath. Often lying flat on your back is a bit restrictive and you need to support yourself along a bolster, a recliner, or even upright with your back against support. A position that allows your spine to be in a long straight line, not curved or extended, is what you are going for. Mess around with where your long spine and your breath meet. Then mess around with this next breath meditation.
The 4-sided breath is an amazing tool to sooth anxiety and stress. It settles the nervous system allowing the brain to feel calm, the body to relax, and the emotions to stabilize.