system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it that sometimes I wake up in the middle of the night feeling refreshed and wide awake, however, if I sleep for a solid 8 hours, I still don't want to get out of bed?
gpt
You have different sleep cycles. So at times your in a very light part of your sleep, and other time your in the REM (rapid eye movment) or dreaming part of your rest and thats a very deep sleep. 

So when you wake up natually during the night your most likely in a very light sleep. Other times when your building a go kart with your ex-landlord and you wake up feeling like shit the REM cycle of your sleep has been disrupted. 

Theres also various apps that will wake you up on the lighter parts of your sleep.