system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Is there a difference between having two 4-hour sleeps or having one 8-hour sleep? Why?
gpt
There are four stages of sleep. The last one, REM (rapid eye movement) sleep, is what really counts because it's when you really get to rest and recuperate. However, to get there you have to go through the earlier stages and then back out to wake up. If you sleep for 8 hours straight then you spend more time in REM sleep than you would with two 4 hour sleeps.