Professor Idzikowski also examined the effect of various sleeping positions on health.
He concluded that the freefall position was good for digestion, while the starfish and soldier positions were more likely to lead to snoring and a bad night's sleep.
Professor Idzikowski said: "Lying down flat means that stomach contents can more readily be worked back up into the mouth, while those who lie on their back may end up snoring and breathing less well during the night.
"Both these postures may not necessarily awaken the sleeper but could cause a less refreshing night's sleep."
The research also found that most people are unlikely to change their sleeping position. Just 5% said they sleep in a different position every night.