The relationship between pain modifying factors, pain duration, and the role of anxiety in low-back pain experience were studied. Three groups of patients with low-back pain were examined using the Tourniquet Pain Test, McGill Pain Questionnaire, Rating Scale of Pain Intensity, State-Trait Anxiety Inventory, and Psychological Discomfort Questionnaire. Significant differences in all measured features emerged between acute and chronic pain groups. Groups of acute and subchronic pain and groups of subchronic and chronic pain differed only in several parameters, suggesting an intermittent phase in acute pain transition into chronicity. While pain prolonged, pain experience gradually but irregularly changed, exaggerating pain perception. The changes concerned mainly emotional factors and were related to the chronicity itself. Anxiety also played a significant role.