Waking up with back pain is commonly caused by several factors related to sleep habits, mattress quality, and underlying health conditions. Poor sleeping positions that strain the spine, such as sleeping on the stomach or in twisted postures, can cause morning back pain. An old or unsupportive mattress that does not properly support the back can also lead to discomfort. Additionally, medical conditions like degenerative disc disease, fibromyalgia, spinal stenosis, or herniated discs can cause back pain that is worse in the morning due to pressure on the spine and nerves during sleep. Adjusting sleep posture, using a supportive mattress, and addressing any underlying conditions are key to relieving this pain.