Blood oxygen levels during sleep should be at a 95 percent saturation, which is considered normal, according to the American Sleep Apnea Association (AASM).
It is normal for blood oxygen levels to decrease during sleep. All body systems have altered basal function during your sleep, including breathing. You don’t breathe as deeply when you are sleeping, and not all your lung spaces function at full capacity. Because of this effect of sleep on breathing, it is normal for your sleep oxygen level to decrease below awake levels. Tests that show a waking oxygen level at or above 94 percent typically indicate a sleep oxygen level of at or above 88 percent.