SPOILER ALERT!
“Out of the blue” panic attacks are usually preceded by specific physiological changes
Irregular breathing patterns and elevated heart rates occur below the level of consciousness before an “out of the blue” panic attack. They are “mini” panic attacks
When those “mini’ panic attacks repeat, a more intense panic attack follows, which is the “out of the blue” panic attack
“Out of the blue” panic attacks (PAs) are believed to occur spontaneously without any warning signs, such as internal sensations or external triggers. By contrast, “cued” PAs (i.e., panic attacks that are expected) occur following a distinct set of physiological changes that vary from person to person.
Physiological changes immediately before a panic attack
For example, one study reports increases in heart rates and skin conductance (i.e., a sign of arousal) prior to the onset of a PA. Increased muscle tension was also observed in laboratory recordings before and during spontaneous and induced PAs (i.e., in a lab, a panic attack can be induced with the infusion of sodium lactate or breathing air full of carbon dioxide -CO2).
Similarly, patterns of changes in heart rates and blood pressure have been noted in another study, although the patterns were inconsistent.
Those results beg the question of whether detectable physiological changes do occur during spontaneous panic attacks as they do in cued PAs.
Undetected physiological instabilities present before spontaneous PAs
Assessing panic disorder patients with ambulatory physiological monitors reveal the presence of significant cardio-respiratory instabilities one hour prior to the onset of a spontaneous PA. Particularly, it was found that those instabilities were triggered by heart rate accelerations, which in turn produced respiratory changes.
Those subtle changes occurred in bouts prior to the onset of the spontaneous PA. By contrast, the period surrounding the onset of the PA was dominated by respiratory changes involving tidal volume (i.e., the amount of air moved during inspiration and expiration) and PCo2 (i.e., measures the level of Co2 in the blood).
Specifically, before panic onset the volume of air inhaled and exhaled decreased while the level of Co2 in the blood increases (PCo2). Then, PCo2 levels remain stable before they decrease further. More importantly, at panic onset those levels drop completely as heart rates and tidal volume increase.
In general those cardio-respiratory changes were detected 47 minutes prior to the onset of a spontaneous PA, which suggests that they were too small to be perceived by the sufferer.
Indeed, it is proposed that those changes are the manifestations of “mini” panic attacks that occur below the individual’s perception threshold thanks to spontaneous respiratory adjustments. However, with repetition, the cumulative effect of those irregularities begins to nudge the interoceptive receptors (i.e., receptors in your joints and muscles) thereby raising awareness to the changes, which in turn trigger a panic attack.
Reference:
Meuret, A. E., Rosenfield, D., Wilhelm, F. H., Zhou, E., Conrad, A., Ritz, T., & Roth, W. T. (2011). Do unexpected panic attacks occur spontaneously?. Biological psychiatry, 70(10), 985–991. https://doi.org/10.1016/j.biopsych.2011.05.027