system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does falling asleep actually work; why can you be mid-thought and just conk out?
gpt
Sleep is a specific action your brain does.

It isn't initiated by the part of your brain that you are actively thinking with.

So, falling asleep mid thought just means that the rest of your brain decided the sleep activity was more important, and told your thinking brain to get in on the party.

Notably, it is more likely it is more gradual than you experience, but the memory part stopped encoding memories of the thoughts. So the experience is sudden... because you suddenly no longer have access to the memories.