There are a number of potential causes for this, so figuring it out requires a process of elimination. Think back to the moment: Were you simply scared awake by nightmares? Another unpleasant but relatively harmless thing that can wake you up this way is anxiety—strong emotions related to stress can trigger a rapid heart rate. As for more physical causes, certain medications—like some asthma treatments—can make your heart race. (Ask your doc if changing or adjusting the medication is possible.) If you regularly skip meals, or if you are diabetic and take medication to control your blood sugar, sometimes your sugar can drop too low, making your heart pound.