Dyspnea is a key symptom in panic attacks. This study investigated different types of dyspnea induced by the 35% CO2 challenge test given to patients with panic disorder (PD). The types of dyspnea provide room for possible conjectures on neurophysiological pathways involved in the experience of breathing discomfort in PD and in the panic-respiration connection. Factor analysis applied to the Dyspnea Questionnaire identified three main factors: breathing effort, sense of suffocation, and rapid breath. Factor scores for breathing effort and sense of suffocation significantly discriminated between patients who did and those who did not report CO2-induced panic attacks. Factor scores for breathing effort significantly discriminated between patients whose reaction resembled their unexpected panic attacks and those whose reaction did not. A dissociation between an increased central respiratory command and a decreased mechanical efficiency of the respiratory response in patients with PD may underlie the breathing effort factor during the CO2 challenge. The sense of suffocation factor was found to be linked to chemosensitivity. Although involved in CO2 reactivity, it may not be a central factor in unexpected panic attacks.