system
Given the following post, respond as if you're commenting on Reddit:
human
If I wake up from sleep, and try to go back to sleep, does my "sleep cycle" reset, or pick up where it left off?

Does it matter what point of the sleep cycle I was in when I woke up, or how long I was asleep to begin with? Does it matter how long it takes me to fall back asleep?
gpt
The interesting thing is that our natural sleep cycle includes a period of wakefulness.  Before the advent of electricity and the lightbulb, it was very much natural for people to have a split sleep cycle, called bimodal or segmented sleep.  They would sleep for several hours once the sun went down, wake up in the middle of the night to visit, eat, work, (have sex), and then return to sleep in the pre-dawn hours.  Only with the invention of the lightbulb do we see the push for a "healthy" eight hour sleep pattern, which is actually quite unnatural and may be the cause of many sleep disorders in modern society.  For more on the subject see At Day's Close: Nights in Times Past by Roger Ekirch - it's a very interesting read.