Ive done a little research on it and found this
"Determine what triggers your sleep paralysis. Sleep paralysis can be triggered by a variety of situations. Some researchers agree that sleep paralysis is most commonly caused by the position you fall asleep in, most commonly when lying on your back. Often, triggers can be factors in your life that you have no control over, such as stress, environment, or even your dreams. Try keeping a log of the conditions of your episode of paralysis. Track details of the experience, the time, your sleep pattern, sleeping position, mental/emotional state before and after you were paralyzed, and if you were paralyzed while falling asleep or upon waking up. This can all be useful information, especially if you decide to see a doctor about the condition."
Me pearsonally it happens most often if I fall asleep with the T.V. on or some noises in the background. It still happens to me alot though either with or without the T.V. so I should probably see a doctor but I've learned to deal with it and how to wake myself up during it.