Take a half dome, or a tightly rolled towel or blanket, place it just at the bottom of your shoulder blades, have a block or book handy to rest your head on.
Do lie like this, see how the lower ribs are down and the back of the neck is long? This reveals the tension in the shoulder girdle which will cause the arms and shoulders to lift a little or a lot. Hanging out here for 5 minutes or so will start to release the tension of the upper back and shoulder girdle. If this is too uncomfortable for your shoulders, just lay your hands on your lower ribs. Find a place where you can relax into the sensations and BREATHE fully, focus on lengthening your exhalations.
Do Not lie down like this!!! See how the ribs and chin are up? This is creating more tension in the lower back, neck and shoulders.