system
Given the following post, respond as if you're commenting on Reddit:
human
What happens when you "zone out" and why do we do it?

Why do we zone out? An example of this is when I'll be doing homework or be reading something and I'll just get blurry vision and just sit there.
gpt
"Zoning out" is a common form of microsleep, which the brain begins to experience after a combination of lack of sleep and a high amount of use (such as a lot of thinking during work, school, or other activities). This is especially so if you're repeating the same task over and over, as the brain goes into "auto" mode, which is also why it is often linked to boredom.

Microsleep is named so because it only lasts about two seconds to less than a minute.

Additionally, if the person is under emotional distress, or has something "on their mind" that is pertinent to their well-being (or they think it is), they are more prone to experience "zoning out," as their mind is more likely to enter into a state of deep thought, connecting their conscious mind to their subconscious, much like just before or during sleep. This is also why people seem to "come to a conclusion" just as they're drifting off into sleep. 

Hope that helps answer your question!