Diluted ammonia and acetic acid served as conditional odor cues (CSs) in a differential associative learning paradigm. Hyperventilation-induced hypocapnia (unconditional stimulus [US]) was used to induce lightheadedness. In a training phase, participants (n = 28) performed three hypocapnic and three normocapnic overbreathing trials of 60 seconds each. One odor was consistently paired with the hypocapnic overbreathing (CS+); the other (control) odor was paired with normocapnic overbreathing (CS-). In the test phase, each odor was presented once during spontaneous breathing and once during normocapnic overventilation. Lightheadedness was assessed online during each breathing trial, which was followed by an extensive hyperventilation symptom checklist. Fractional end-tidal CO2, breathing frequency, and inspiratory volume were measured throughout the experiment.