In the pulmonary circulation low oxygen levels causes

Lung diseases such as chronic obstructive pulmonary disease (COPD), emphysema, bronchitis, pneumonia, and pulmonary edema (fluid in the lungs) Strong pain medicines and other drugs that hold back breathing. Heart problems.Anemia (a low number of red blood cells, which carry oxygen)

Atp is is our little "pocket" of energy. of course, if you have too little, then it means you have too little energy, and you'll pass out. the way to not have enough, is to have no energy sources (glucose, fats, proteins). you can't have too many atp molecules. cycles like the krebs cycle produce it, but if you have too much of any substrate (or too little for that matter), the cycle stops and atp is no longer made (it stops until substrate levels are such that the process can go on). in any case, this is unlikely since atp is constantly hydrolyzed and remade, even while you're asleep. you won't have too much. if you have zero, you are dead or dying.

Vijina kid