"Calculated tiredness" in the first night you barely sleep?

Hey,
I know generally not getting enough sleep at night makes it really hard to have lucid dreams or even gain proper dream recall. What I noticed is that often after getting a fair amount of sleep every night even for weeks (and having at least somewhat lucid dreams) the first night I sleep like 6 hours only I never have any lucid dreams. But how can this be a problem of being to tired when I go to bed at the same time and enter my rem cycle (first around 3:30) at the same time as all the nights before. Up until I have to get up I shouldn't be any more tired than before, no? I understand why I'm not having any lucid dreams the second night because I'm already tired when I go to bed and usually fall asleep right away without having a chance to repeat my mantra and clear my head... I was wondering if that could maybe be some perceptual memory thing like my brain already knew it wouldn't get a whole lot of sleep that night when I set the alarm and thus "acted" tired to "save energy" maybe? It happens that you wake up a minute before your alarm, or wake up in time even though you forgot to set an alarm, right?
Could this be something like that?

Hope you guys know more about this than I do:)

Maybe your lds are after the 6th hour of sleep? Or if you know you will get only 6 hrs of sleep, you are thinking, I won't be getting enough sleep to ld, therefore setting a negative intention?

Welcome to DV! :)

I sometimes wake up around the forth hour of sleep and already remember dreams from then so I think that's not it but I guess it could simply be a negative intention rather than some of that deep supconscious stuff haha
and Thanks!