system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do our faces look so weird and tired when we wake up?

Why do our faces look bloated and eyes all puffy when we first wake up? What's taking place in its tissues to cause this and is there a way to speed up recovery?
gpt
More concentrated blood In different locations. All day you are standing up and walking around, and our body is built for that. Our veins have tiny one way valves that let blood go up but not back down to reach the head. 

When we sleep, that blood needs much less effort to go to the head. So there's more blood, think of it like completely harmless swelling. Just standing up and walking around will get everything back to normal.