Several things can cause a person's oxygen level to drop including things such as chronic obstructive pulmonary disease, emphysema, bronchitis, pneumonia, and pulmonary edema (fluid in the lungs).
Even some pain medicines that are pretty strong can sometimes cause a person's oxygen level to drop as well.
If your oxygen level drops to low it can lead to death so get treatment for the low oxygen level if you think your oxygen level is too low.
You need the correct oxygen level and enough oxygen to survive and if you do get too low on oxygen you can even get brain damage as a result.
A persons normal arterial oxygen level is approximately 75 to 100 millimeters of mercury (mm Hg).
And oxygen level values under 60 mm Hg usually indicate the need for supplemental oxygen.