You have to wake up at the end of a REM cycle, or you’ll wake up feeling groggy and tired.

Have you tried 12 hours?

I do pretty much always wake up tired, but I also can’t make myself stay awake past 9 most of the time any longer. Not since I hit 40 or so (46 now). I used to be able to stay up all night if I wanted to. This is the first year in a while I was able to stay up until midnight to see in the new year. And just barely.

My sweet spot really seems to be 6hrs. I feel most alert and functional. At least for the past 5 years or so.

Prior to that I worked 2 x 24hr shifts, many times 3 x 24hrs, per week. My sleep was a significantly different pattern.

10 hours is too much. I find 7 is the sweet spot for me.