the main condition that comes to mind is obstructive sleep apnea (osa) though congestive heart failure (chf) or even chronic obstructive pulmonary disorder (copd) also could cause nocturnal hypoxemia (abnormally low blood oxygen levels at night). if you believe you have abnormally low oxygen levels during sleep i'd strongly suggest you have this symptom checked out by a medical professional. untreated hypoxemia can have negative health consequences. hope this helps!
what type of underlying health problems can cause oxygen levels to drop at nighttime?