Sleeping supine is often the cause of apnea
The Obstructive Sleep Apnea Syndrome (OSAS), which is also simply called (sleep) apnea, is disturbed breathing during sleep which causes breathing to stop. The consequences of this include severe tiredness, lack of concentration, irritability and an increased risk of heart failure.
Sleep apnea occurs for the majority of people when they are supine. Your tongue relaxes and, when supine, falls backwards easier due to its weight causing the airway to be blocked. This is called positional sleep apnea. Over half of apnea patients have positional sleep apnea. Within this category sleep apnea is at least two times worse when supine than in any other position. In another approximately 30% of patients sleeping on the back is considerably worse, but not with this factor two difference