Carbon dioxide is more than a by-product of respiration. It's also the stimulant that tells you to breathe. This is why your breathing rate varies according to your activity level. Your body produces carbon dioxide faster during heavy activity, so your body receives the signal to breathe more often than it does at rest.

If the levels of carbon dioxide become too high, you can suffer symptoms of carbon dioxide excess. Symptoms include panic, breathlessness, dizziness, headaches, or even unconsciousness.

To safely control the levels of carbon dioxide in your bloodstream, you should breathe slightly slower and deeper when diving.