system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What happens in the brain when someone is daydreaming and what neurological activity(ies) causes someone to come out of it?
gpt
Daydreaming is focusing conscious neurological power on a memory or a fabricated idea...the brain has the ability to compute multiple areas of attention and information every second, this allows you to underlying continue the task at hand while considering and embracing other thoughts.

 It was originally and instinctual survival skill (chasing, while throwing or grabbing or planning your next move) and through the evolution of communication and culture, your brain can now calculate multiple tasks that you desire at one time. Basically your are telling you brain to be aware of your current surroundings/situation while allowing the neurons to fire and create a fabricated idea/visualization to focus the majority of your mental power on.

Edit - coming out of a daydream is usually a product of subconscious override that your current situation demands your attention, usually to keep you safe either physically, mentally or emotionally... However it can be provoked purposely if you decide to shift your focus to either another daydream, thought or progressive idea.