Infusion procedure: Subjects will be recumbent in bed and made comfortable In intravenous line will be placed in the antecubital fossa and a slow intravenous infusion of 5% dextrose in water (D5W) will be administered for 28 minutes, then accelerated for 2 min. to mimic subsequent lactate infusion. The intravenous solution will be out of view of the subject behind a bedside screen. Subjects are blind to the timing of lactate administration. At time 0 (after 30 min. of D5W infusion), an infusion of 0.5 mol/L sodium DL-lactate (at body temperature) is initiated. The total dose (10 ml/kg body weight) is administered over the subsequent 20 min., unless the subject experiences a panic attack, in which case the lactate infusion is immediately discontinued. At the time of panic symptoms, or at the end of 20 min., the subject is switched back to D5W for 5 min., followed by termination of the infusion.