This is entirely possible when the sleep becomes "too deep." Newborns experience it and occasionally die from it. People intoxicated with alcohol or other drugs also find themselves in situations where their normal reflexes are impaired and they do not react to soft tissue obstructing their airway. Every day there are people being intubated in EDs because of their unability to protect their airway. It is likely that this is happening somewhere in the nation as I write this.