A patient has a history of occasional, mild tension-type headaches. Over the last year, the headaches have become a daily occurrence, described as a constant, dull, bilateral pain. The patient also reports that now, even a gentle massage of the neck and scalp, which used to be soothing, can sometimes feel intensely painful. Based on the described physiological mechanism of chronic tension-type headaches, explain the neurological changes that would account for this patient's transition from occasional headaches to persistent, daily pain with increased sensitivity.