Several things can cause your bodies oxygen level to drop such as low oxygen levels in the air you breathe, lung issues that make it hard for your lungs to breathe in enough oxygen.
Your lungs take in the air and circulate oxygen through your bloodstream and sometimes your lungs can have issues and make it hard for the lungs to provide enough oxygen through your blood.
Being a smoker damages your lungs as well and cause cause low oxygen levels.
Low oxygen levels can be dangerous if the oxygen levels in your body get way too low.
The normal oxygen level reading should be between and in a range of 75 to 100 millimeters of mercury (mm Hg)
If your oxygen level drops slightly below that level then there's likely not a serious health issue and you likely have nothing to worry about.
But when your oxygen levels get way too low then it can cause serious health issues and may even cause death and brain damage.
If you think your oxygen levels are too low then you need to see a doctor or go to urgent care for treatment to get your oxygen levels back up.
You may need to use oxygen to breathe properly if your oxygen levels drop way too low or stay too low.
Oxygen levels can sometimes drop a little which is normal but they should not drop a whole lot.