I recently flew with my POC. I felt great and did not use it hardly at all.
Even though i was feeling good and taking deep breaths (and PLB'ing), my pulse oximeter was indicating O2 sats in the 70's and low 80's.
I know what that feels like and knew that my oximeter was giving bad info - at least i am 90% sure.
I bought new batteries and my numbers are great.
Could that have been as simple as the batteries or was there something in the cabin pressure and altitude have had a positive effect on my oxygen?