There are three main sleeping positions with variables of each: side, back, and stomach. Sleep specialists recommend sleeping on your side in order to rest more comfortably and decrease the likelihood of interrupted sleep. While there are many variations of sleeping on your side, all of which are beneficial in helping to alleviate insomnia and chronic sleep deprivation, the most comfortable position involves bending the knees slightly upwards towards the chest area. For those with a bad back, consider placing a pillow between your legs to alleviate pressure on your hips and lower back. Sleeping on your side is actually encouraged for those suffering from back or hip pain or pregnant women, since this position doesn’t increase pain in these areas.

Back position - Sleepers who lie on their backs with arms up near their head or the pillow account for 5% of participants. These people are good listeners, helpful, and are uncomfortable being the center of attention. People who sleep in starfish position are more likely to snore and to suffer from a poor night's sleep more often.

stomach position - Those people who lie on their bellies with arms under or wrapped around a pillow with head turned to the side, make up 7% of the population studied. Freefallers are brash, outgoing, and are very uncomfortable with criticism.

Soldier position- These sleepers lie on their backs with arms down and kept close to the body. This 8% study is said to be reserved, quiet, without fuss, and hold themselves and others to a high standard. Soldier sleepers have a higher likelihood for snoring due to the flat-back position, which may not cause them to wake up often but may result in a less restful night's sleep.

Log position - If you sleep on your side with both arms down, you are a social, easy-going person who is trusting, sometimes to the point of being gullible. The study showed 15% of people sleep like a log.

Fetus position - A whopping 41% of participants sleep in this curled-up manner. Women are twice as likely to rest like this and it is listed as the most common position. These sleepers are said to have a tough exterior but are still sensitive and may appear to be shy but warm up quickly.
CREDIT :http://www.jennygist.com/2015/09/best-and-worst-sleeping-position.html

so one should be mindful of he or she is lying while sleeping? hmmmmm that means you are not sleeping because if actually you are sleeping you wouldn't even know when you will cover all those positions.