system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does closing eyes when tired feel good?
gpt
The biggest reason is because when your body starts to prepare for sleep, one of the things it does is it starts producing less tears. This is because it is expecting you to close your eyes and keep them closed for a while, so it shouldn't have to do as much work washing the eyes.

If you push past this and keep your eyes open and stay awake even when your body wants to sleep, your eyes tend to get dry and irritated. At which point closing them lubricates them up again and feels pretty damn good.