system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What causes us to wake up right before the alarm goes off?

I never have problems sleeping through an alarm because I always wake up right before an alarm even though I have different alarm times almost every day. Why and how does this happen?
gpt
Your body has proteins that act like grains in an hourglass. When they run low your body knows it's time to go to sleep. While you sleep the hourglass fills back up until it's full enough that your body starts to wake up.

If you keep a regular schedule, your body's natural cycle will start to sync with your artificial cycle (the alarm clock)...so your body will start to naturally wake up at the same time your alarm clock is set to wake you up.