When you get up every morning with back pain, but after daily activities during the day your back does not hurt again, this situation is mainly to consider the existence of lumbar muscle strain. Maybe the lumbar muscle strain is not serious, just a mild congestion and edema of the lumbar muscle. Due to the presence of congestion and edema in the lumbar muscle, the local blood pooling in the flat position at night, coupled with low blood pressure during sleep, resulting in poor local venous return of the lumbar muscle, the symptoms will be aggravated in the morning when you get up and have pain. After activity, local blood circulation is restored, coupled with the daytime blood pressure is higher than when sleeping, resulting in local blood circulation is not greatly affected, the pain symptoms will be very light or not. At night, the blood pressure drops and the local blood pooling due to gravity causes the aggravation of the strain symptoms.