Some people who are quite overweight, who have lung or heart problems, or who have medical problems that make them breathe too shallowly (SLEEP-RELATED HYPOVENTILATION) may have repeated serious drops in their oxygen levels during sleep--even though they may never actually stop breathing.

They simply do not breathe deeply enough to maintain good blood oxygen levels.

Failure to generate adequate breathing effort--whether due to central sleep apnea or sleep-related hypoventilation--can occur without snoring, breathing pauses or any symptoms...even when severe to the point of causing progressive heart damage from lack of oxygen in the blood.