What are Snoring and Sleep Apnea?
Snoring is almost always caused by a restricted airflow at the back of the throat. This happens when the jaw (and attached tongue, which is much larger than just the part we see) falls to the back of the mouth, so air has to be forced between the tongue and the back of the throat. This makes the throat to vibrate loudly - causing snoring.
Obstructive Sleep Apnea is when the airflow is so restricted the throat completely closes, stopping breathing. This triggers a choke reflex to clear the airway, disrupting sleep. More on sleep apnea...
Snoring and sleep apnea happen when asleep because the jaw muscles go slack, so the jaw (and the attached tongue) fall back, narrowing the airway.
This effect is made worse by laying on your back, causing the jaw to fall back more. Snoring is also worse when overweight, or relaxed after a drink or two.