Without the required oxygen saturation level, you might experience shortness of breath, headache, and confusion or restlessness. Because Hypoxemia is more likely to occur when you’re stressed from exercise or illness, you should carry a finger pulse oximeter monitor when mountain climbing, running, biking, etc. They’re easy to carry and use.
https://www.amazon.com/Oxygen-Concentrator/s?k=Oxygen+Concentrator