system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How big is the divide between sleeping and not sleeping?

Ever since I was a child, I would think about how I could never pinpoint the exact moment that I fall asleep. What exactly is the separation between being awake and being asleep from a neurological standpoint.
Is it a sudden switch, or does it happen gradually? If it's gradual when can we label someone as asleep rather than awake?
gpt
Sleep researcher here: there is a short transitionary phase which lasts about ten minutes when you first go to sleep known as stage 1 sleep (associated with a hypnagogic state) after which you then go into deep sleep (stages 2-3).