system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 - Why does someone wake up feeling more tired after a lot/good night of sleep but feels more awake after a little/bad night of sleep?
gpt
To get into a nice deep restful sleep your brain has to release lots of chemicals that make you sleepy. 

When you wake up you are still clearing out those chemicals so you are drowsy. 

If you don't get down into that deep sleep then you have less of those chemicals to clear out so you aren't as drowsy.