We briefly reference previous material on Klein's suffocation false alarm theory (SFA) of panic disorder (Klein, 1993) and its amplification in 2008 (Preter andKlein, 2008). We then discuss a recent finding showing a fundamental difference in opioidergic reactivity to a naloxone challenge in psychiatrically and medically healthy adults, based on the presence or absence of childhood separation/parental loss.In 1993, Klein published the original SFA theory of panic disorder (Klein, 1993), attempting to integrate the multiplicity of apparently unrelated clinical and laboratory observations. We posited "that a physiologic misinterpretation by a suffocation monitor misfires an evolved suffocation alarm system. This produces sudden respiratory distress followed swiftly by a brief hyperventilation, panic, and the urge to flee. Carbon dioxide hypersensitivity is seen as due to the deranged suffocation alarm monitor. If other indicators of potential suffocation provoke panic, this theoretical extension is supported." In the original paper, we tested "the theory by examining Ondine's curse as the physiologic and pharmacologic converse of panic disorder, splitting panic in terms of symptomatology and challenge studies, reevaluating the role of hyperventilation, and reinterpreting the contagiousness of sighing and yawning, as well as mass hysteria." (Klein, 1993) Original SFA focused on relating the observed lactate and carbon dioxide hypersensitivity in panic disorder to a putative dysfunction in a hypothesized suffocation alarm. At the time, the underlying pathophysiology that might connect the apparent disparate "phenomena of panic during relaxation and sleep, late luteal phase dysphoric disorder, pregnancy, childbirth, pulmonary disease, separation anxiety, and treatment", was unknown.