Summarize:

One of the major causes of morning back pain is a poor sleeping position during the night. Like sitting with poor posture in a chair all day, sleeping in a poor position all night will cause your back to become stiff and tense, leading to back pain in the morning (think about it: that's eight hours in a position that strains your back). Though it may be difficult to train your body to embrace a different sleep position than customary, it is worth doing as a way to prevent morning back pain.  Try to sleep on one side with your legs bent and tucked towards your chest. You can also place your hands by your head or under your pillow. This fetal sleeping position will put very little stress on your back and help to prevent stiffness and discomfort in the morning. You may also want to place a pillow between your legs while you lay on your side to help release tension in your lower back. Tuck the pillow between your knees and let your legs relax. If you tend to get the best sleep when sleep on your back, slide a pillow or a rolled towel under your knees before going to bed. This will help to relieve any stress or tension on your back as you sleep. If you are a light sleeper and tend to wake up throughout the night, make an effort to shift your sleep position so your back is better supported. This could mean moving from sleeping on your back to sleeping on one side in the fetal position. Or, you may place a pillow on either end of the bed to prevent you from rolling around onto your stomach or your back during the night. Over time, your body may adapt on its own to a sleep position that is better for your back. You should make sure you are sleeping on a good quality mattress that is not sagging in certain areas or lumpy. A good mattress can help to provide good support for your back as you sleep, especially if you tend to sleep on your back. You may want to invest in a mattress pad that you can place over your mattress to make it more comfortable and smooth, or consider getting a new mattress if your mattress is getting old and starting to sag. Sometimes, the wrong temperature can have effects on back pain and tightness. For example, workers in cold environments are at greater risk of developing low back pain. Pay attention to room temperature and make sure you sleep in a comfortable setting. If your room is cold, try to increase the size of the comforter or blanket. Cold temperature at night can tighten up the muscles and lead to muscle aches in the morning.  You may also want to see if your room is damp or too hot also. Not everyone will react to the same temperature the same way.
Try to sleep on one side in the fetal position. Put a pillow or a rolled towel under your knees if you tend to sleep on your back. Adjust your sleep position if you wake up during the night. Check that your mattress does not sag or have lumps. Pay attention to the temperature in the room.