You can be dehydrated, in a bus, coming back from work, the air conditioner not working probably... The line between napping and fainting is an ambiguous one.
Snorers often suffer from sleep apnea. Tissue blocks their air ways which basically causes them to suffocate. This reduces the oxygen concentration in the blood which causes damage to your organs and not restful sleeps
Bodybuilders often suffer from that due to their big necks. So they have to use breathing help helpers in their sleep.