system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we stretch when we're tired at night and when we wake up in the morning?

and why does it feel so good?

edit, thanks guys! It also brought up some more interesting questions.
gpt
*Circulation!*

Stretching improves blood circulation in your muscles which helps your body regulate your heart rate (for sleeping or waking up), and it feels GREAT!

Don't listen to the BS about calcium in your bones (/u/calzoner), its nonsense.