system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do I get tired from oversleeping?
gpt
You might be tired because you woke up in the middle of your sleep cycle. As the night goes on, the body will go through stages of sleep; and the deepest is REM sleep. That's where all your dreaming happens. An average sleeping cycle lasts approximately 90 minutes. If you wake up in the middle of one of the cycles, it can leave you feeling extremely groggy.