system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can contact lenses be worn all day without issue, but nap with them in for an hour and they get glued to one's eyeballs and one's eyes get gunky.
gpt
The eye is a self cleaning mechanism.  That's what blinking and tears are all about.  However, this mechanism is shut down during sleep, so your eyes stay shut.  Contacts irritate the eye, but you can learn to tolerate it.  However, without the cleaning mechanism, the irritation is much more painful.