O2 at Night?

Eric is getting sneaky. He slept without his O2 last night and didn't tell Bob and me. When Bob checked on him this morning, he found Eric with the O2 off. Bob checked Eric's pulse ox and it was 97%, which is great, but Eric was already awake then. We don't know what it does when he sleeps. He had it on getting ready for bed, and we heard the concentrator running all night, so we assumed it was in his nose. Eric said he deliberately took it off. I don't blame him for not wanting it on at night. But, admittedly, he didn't sleep well last night, and we don't know if that's an O2 issue or a coincidence. We'll leave it off again tonight, but with the pulse oximeter on, so we'll know if his saturation drops below 92%.