Sleep is fun, people who regularly lack it will tell you they're "just fine" but they've been lacking sleep for so long that the baseline they're comparing themselves to is already skewed. Take two weeks off, avoid alcohol and other stimulant, avoid artificial light after 8 and wake up without an alarm. You'll see how you feel after that regimen. Your body knows exactly how much sleep it needs. But that's not compati…
I dunno, maybe I’m weird, but without an alarm I can sleep 12 hours. And when I do, I feel like total shit: very tired, groggy, and a little depressed. If I sleep 5-7 hours on the otherhand, I feel much better.
Try to increase your bedtime slowly to 8 hours, maybe 9(but not much more than that) and keep at that for a while. See if there is any benefit.
It is unlikely that you are part of the tiny minority that requires less than 6 hours of sleep, so you should be sleep-deprived with only 5 hours.
Personal anecdote: my sleep patterns were very similar. Until I got diagnosed with sleep apnea. My body wanted more sleep – but the more I slept, the more apnea events I would have. So, I would wake up feeling like death, and with a headache, due to my brain getting starved of oxygen.
Not saying that this is your problem or that there is even a problem, but you could raise this issue on your next checkup. Maybe your doctor will have some suggestions.
Because it is weird, as you rightly point out. Trust your judgement.