Muscle strain, bad posture, stress, heavy labour, lack of sleep, and occasionally nerve or spine issues can all cause severe back pain and tightness throughout the body. Apply a warm compress, stretch gently, avoid heavy lifting, take a brief break, drink plenty of water, and sit or sleep with proper posture. The body can also become extremely tense due to stress and anxiety. You should consult a doctor for an appropriate diagnosis and treatment if the pain is severe, spreading to the legs, accompanied by numbness, weakness, fever, or problems passing urine.