Most acute pain in the back results from sustaining a mild strain in the back or back musculature. Sprains and strains in your lower back usually happen during a sudden and stressful injury, causing stretching or tearing of the muscles, tendons, or ligaments in your lower back. When you strain or sprain your lower back it causes a lot of stress on your spine, irritating it. If you have this condition you may also suffer from painful muscle spasms which can occur during your daily activities or at night while you're sleeping. The pain is usually limited to five or ten days.