Breathing in too deeply, especially in a short period, can lead to a condition called hyperventilation. Hyperventilation is characterized by rapid and/or deep breathing that results in an excess of oxygen in the blood and a decrease in the level of carbon dioxide (CO2). This imbalance can cause symptoms such as dizziness, lightheadedness, shortness of breath, and even fainting. The body relies on a proper balance of oxygen and CO2 to function correctly. When you breathe deeply or quickly, you give off more CO2, which can lead to a state where there is not enough CO2 for the body's needs. In hyperventilation situations, you breathe off even more CO2, so the body utilizes less oxygen. This is similar to what happens when you have run too hard and might experience lightheadedness due to the rapid breathing that occurs during the exertion. read more >>

So not enough CO2 means your brain and body don't get enough oxygen. ... If you breathe deeply or quickly you give off more CO2. In hyperventilation situations you breathe off even more, so the body utilizes less oxygen. Think of when you have run too hard.read more >>