system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we wake up with morning face?

Puffy eyes, fat face.
gpt
When you're up and about and walking around,  your heart has to work against gravity to pump blood up into your face. But when you have been laying horizontal in a bed for 8 or so hours it gives blood the opportunity to "pool" or "settle" in your face, resulting in puffiness. You'll get a more extreme example of this if you hang upside down for an extended period of time.