system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why does our brain sometimes wake us up during the night, despite there being no external stimulus, and when we clearly have not had enough sleep?
gpt
Depends. What kind of waking up are you talking about?
The one where you have no chance to go to sleep again (insomnia style) or more like waking up, realizing it’s still bed time, rolling to the side and going back to sleep?