Case 1: When I sleep slightly less than would be ideal, for example less than 7 hours per night, I wake up reasonably functional and get through the day without being excessively tired, if not being totally alert either.
Case 2: When I sleep slighly less than would be ideal, for example less than 7 hours per night and wake up, let the dog out to the backyard, wait a few minutes, let the dog back in, and decide to go back to sleep because it’s weekend. Now falling asleep takes a while but eventually I succeed. Then after an hour or two at max, I wake up again, but this time around I’m extremely drowsy with muscles aching and it takes serious effort to get up and get the engine running at normal speed. Even though the total amount of sleep (about 8-9 hours) sounds pretty ideal on paper.
Why is that?
In case 2 it sounds like you sleep less, or less well. Unfortunately it’s hard to monitor. Devices like Fitbit are better than nothing but are not very accurate.
I do have a Huawei Band 8, but the differences in the stats are not great between nights. Not the most accurate device but it seems to get some things right. I know I should get more deep sleep but it is what it is.