If I am regularly running, my resting heart rate at night drops into the upper 30s. During the day sitting down, 45-50.
If I haven't been running (for a week or longer) it picks back up in to the mid 40s at night, and around 60 for normal sitting.
My heart rate when sleeping is 65bpm, and I can't focus on anuthing if my heart rate is below 90bpm during the day.
Some of the most productive people I know eat nothing but donuts and coffee, and don't exercise at all. They're smart, driven, and highly successful.
Meanwhile, I know a lot of people who put exercise and food as a priority, and don't seem nearly as sharp or as successful. Maybe this all washes out, with age.
Point is - do whatever works for you. Don't let some blog, or some person on the internet, tell you how to perform optimally!
Don't ask me how I know :-)