 Furthermore, chronic stress is associated with disrupted circadian restactivity rhythms and domains of quality of life QoL including fatigue, insomnia, and reduced physical and social functioning. Interventions that relieve pain thus represent a novel therapeutic target for normalizing dysfunctional restactivity rhythms and these QoL domains among pain patients. The investigators are also interested in assessing the effects of HRV-B on cognitive function in pain patients. Thus, the investigators secondary exploratory objectives are to determine if HRV-B: 1 improves sleep and restactivity rhythms; 2 alleviates self-reported fatigue and depression; and 3 improves cognitive function reaction time, attention. Circadian endpoints will be measured as actigraphic parameters of sleep e.g., duration, efficiency, and restactivity e.g., dichotomy index, interdaily stability, and with the Insomnia Symptom Questionnaire ISQ; fatigue will be assessed using the Multi-Dimensional Fatigue Inventory MFI, which assesses general physical and mental fatigue and motivation. Depression will be assessed via the Beck Depression Inventory II BDI-II. Cognitive function will be measured with a cognitive battery comprised of the Paced Auditory Serial Addition Test PASAT, the Rey Auditory Verbal Learning Test RAVLT, and the Psychomotor Vigilance Test PVT. 