The left side of the neck tendon pain need to be alert to fall asleep, soft tissue injury, cervical spondylosis, muscle strain and other diseases. 1. Falling pillow: due to sleep posture or pillow discomfort, the neck is in excessive flexion and extension, causing excessive tension in the neck and shoulder muscles, and the head may be tilted to the side in the morning, and one side of the neck and shoulder pain is often accompanied by activity limitation. 2. Soft tissue injury: Traumatic injury to the sternocleidomastoid muscle, trapezius muscle and other muscle strains can lead to neck pain on the left side of the tendon. 3. cervical spondylosis: due to cervical spine degenerative disease resulting in osteophytes, ligament thickening or disc herniation, compression of the left side of the soft tissues, nerves, blood vessels can lead to the left side of the neck tendon pain, often accompanied by reflexive pain or numbness of the upper limbs. 4. Muscle strain: due to long-term low head work or other bad posture can lead to the neck and shoulder muscles in a state of long-term tightness, can appear in the left side of the neck tendon pain. There may be other reasons for the left side of the neck tendon pain, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to carry out the appropriate treatment.