Hyperventilation is defined as ventilation in excess of metabolic requirements that leads to a reduction in partial pressure of arterial carbon dioxide (PaCO₂), leading to symptoms of dyspnea, paresthesias, tetany, dizziness, headaches, visual disturbances, and atypical chest pain. The initiating event in hyperventilation leads to increased alveolar ventilation with subsequent drop in PaCO₂ to approximately 20 mm Hg.

The initial drop in PaCO₂ leads to the symptoms described above along with a subsequent increase in minute ventilation to help alleviate the symptoms, only to make them worse with ongoing hyperventilation. Patients with hyperventilation syndrome often undergo an unrevealing medical evaluation for the etiology of their hyperventilation. Many of these patients develop anxiety about the high likelihood and unpredictable nature of potential future hyperventilation attacks.

While anxiety disorders and panic attacks may be both an initiating and sustaining factor for hyperventilation syndrome, they are not necessary for the development of chronic hypocapnia.