I don't know re sleep mode, but it does estimate your caloric burn throughout the day- it does base it off your bmr as far as I know- that's not unusual. So I wouldn't worry about that. I do think it over or underestimates caloric burn for working out, so I use a HRM for that. I DO find it is accurate if your exercise of the day is walking. Feel free to message me if you have more questions!