Hyperventilation or overbreathing is the state of breathing faster or deeper than normal, causing excessive expulsion of circulating carbon dioxide. It can result from a psychological state such as a panic attack, from a physiological condition such as metabolic acidosis, can be brought about by lifestyle risk factors or voluntarily as in the yogic practice of Bhastrika. It often occurs together with labored breathing, which, in contrast, can also be a response to increased carbon dioxide levels.
Hyperventilation can sometimes cause symptoms such as numbness or tingling in the hands, feet and lips, lightheadedness, dizziness, headache, chest pain, flexor spasm of hands and feet, slurred speech, nervous laughter, and sometimes fainting, particularly when accompanied by the Valsalva maneuver.
Counterintuitively, such effects are not precipitated by the sufferer's lack of oxygen or air. Rather, the hyperventilation itself reduces the carbon dioxide concentration of the blood to below its normal level because one is expiring more carbon dioxide than being produced in the body, thereby raising the blood's pH value (making it more alkaline), initiating constriction of the blood vessels which supply the brain, and preventing the transport of oxygen and other molecules necessary for the function of the nervous system. At the same time, hypocapnia causes a higher affinity of oxygen to haemoglobin, known as the Bohr effect, further reducing the amount of oxygen that is made available to the brain.