Is it permissible for me to sleep on my left side?

It was part of the Prophet's guidance (peace and blessings be upon him) to sleep on his right side, placing his right hand under his right cheek. He (peace and blessings be upon him) guided to this by saying: "When you go to your bed, perform ablution as you would for prayer, then lie down on your right side." Among the benefits of sleeping on the right side is that it is quicker to awaken, and the heart, being inclined to the right, is not weighed down by sleep. It is also more beneficial for the body, as one begins by lying on the right side for a while, then turns over to the left. Sleeping on the right side is a Sunnah for which one is rewarded for acting upon, in imitation of the Prophet (peace and blessings be upon him). As for sleeping on the left side, it is permissible, but one misses out on the reward of following the Sunnah.