Your heart rate can change throughout the day based on your level of activity, emotions, stress levels, etc. Stress and exercise increase your heart rate, while relaxing and sleeping can lower it. A normal heart rate while you're sleeping anywhere between 40-50 bpm. Now, if you're familiar with normal heart rates, you may think that's incredibly slow, or what's medically known as bradycardia. But your body is under less metabolic demand when you're sleeping, therefore, you're heart doesn't have to beat as fast. Continue reading to learn more about what is a normal heart rate for different ages, as well as signs that you could have an underlying condition.