I want to emphasize how important it is to measure the blood oxygen saturation level. You can't go by feel on this; you have to measure it. A pulse oximeter is a cheap, accurate and easy-to-use tool to do that. Take a reading every few minutes; it may be your only indication if something is wrong with your oxygen supply.Highly recommend a finger oximeter to measure blood oxygen %. They are inexpensive.
Here is an interview I recorded with Dr. Brent Blue on the topic of oxygen for pilots: