Chemical changes can happen with overbreathing. Hyperventilation causes the carbon dioxide level in the blood to decrease. This lower level of carbon dioxide reduces blood flow to the brain, which may result in the following nervous system and emotional symptoms: 1  Weakness. 2  Fainting. 3  Dizziness. 4  Confusion. 5  Agitation. 6  A feeling of being outside yourself. 7  Seeing images that aren't there. 8  Feeling as if you can't breathe.