22 yo. No sig health history. My heart rate gets as low as 48 when I’m just waking up or falling asleep, normal resting rate during the day when I’m relaxed is 60. Why is my heart rate so low? Not an athlete but not overweight. Eat an ok diet

Hard to say. When physicians don't have a clear answer it is reassuring. For if it were a serious problem more likely we'd have some explanations. My educated guess is that it reflects a drop in your sympathetic tone and as a result your heart rate drops. If you are
without other symptoms likely not a concern. If in my office I might listen to the heart just to assure all sounds ok. .