Shoulder pain lying down and body backward without pain may be caused by muscle strain, myofasciitis, rotator cuff injury and other reasons. 1. Muscle strain: muscle strain around the shoulder, usually sitting and standing and activities, muscle contraction to maintain the stability of the shoulder joint, resulting in significant pain. While lying down and backward, the shoulder is in a relatively relaxed state, often does not produce significant pain. 2. Myofasciitis: When suffering from myofasciitis, the stimulation of inflammation can lead to localized pain in the neck. When lying flat and backward, the fascia is in a relaxed state, which can ease the pain and may not cause significant pain. 3. Rotator cuff injury: When rotator cuff injury occurs in the shoulder, it can lead to partial or complete rupture of the tendon. When standing or sitting, the shoulder may experience significant pain due to the force of gravity. Lying down and lying back, the shoulder is relatively relaxed, which can lead to pain relief. If you have shoulder pain, but not when you lie down or move your body backward, it is recommended that you go to a specialized hospital in time for relevant examinations and treatments.