If you decide to sleep on your side, make sure your head is part way off the side of the pillow so the face mask is not touching the pillow. Otherwise the pillow will push up on the mask, causing it to leak. Sleeping on your side is recommended. Make sure your mask is the proper size. Too small or too big can cause leakage. Be aware if you have an automated machine that switches on and off without you pushing a button, just putting the mask down with the mask facing down can cause the machine to think you are still wearing it and that it is leaking.