the pulse-ox at the hospital I go to has a pre-set alarm that goes off if the level drops below 85%. I usually go by that... Normally I'm around 92% on room air and 95% on 1.5-2L of O2. Mid-80's and I crank up the oxygen until I stabilize. Like others have said, the main concern is for the enormous strain on your heart to re-oxygenate your blood. For example, when I am health and at 94% my heart rate is in the 70s. When I am sucking on O2 and my stats are hovering at 88% my heart rate jumps up to 130. You might want to ask about finding a homecare company that can set you up with an oxygen compressor to use at night. Insurance probably won't give you a problem.