👉 A "bradypnea" is a condition in which the heart rate is so high that it can be felt even during deep sleep. It's usually caused by the body producing too much adrenaline and not enough oxygen, leading to rapid breathing and shortness of breath. Bradypnea often occurs when you are tired or stressed out, but it also happens if your body isn't getting enough rest or if there is a health issue that makes you feel fatigued easily.