system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it hard to wake up at 7 AM but easy to wake up at 10 with the same amount of sleep?
gpt
You always wake easier and feel better if your wake up time is matched to your circadian rhythms and REM cycles.  Everyone has a natural circadian rhythm of roughly 24 hours.  This is influenced over time by your exposure to light and dark, age, physiology, and habits.  Regardless of when you go to bed or wake on a particular day, your body cannot change this cycle quickly or easily.  Ever find you wake up naturally seconds or minutes before your normal alarm?  That's your natural rhythm that your body is currently tuned too.  Even if you go to bed early to try and "rest up", your body may not enter the most restful sleep until it's "usual" nightly schedule, so you don't get the full value of the extra sleep.  On the other side of the equation, waking later than usual is almost always a "Bonus", and so it gives you the full benefit of the extra time after your bodies natural restful sleep cycle.  You can also find it helps to try and determine your REM cycles.  The point in your sleep cycle where you are sleeping lightly, as opposed to the deep REM cycle where you are sleeping deeply and often dreaming.  There are apps for your phone or tablet that may actually work reasonably well to help you predict the best time to wake.  Surprisingly, waking a half hour earlier might be the best time for you as your body comes out of a deep REM cycle.  Wait too long, and it goes back into deep REM again, and waking is more difficult.