system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What causes us to wake up in a bad mood sometimes?

You can fall asleep perfectly fine but still wake up irritable for no apparent reason (even when it's when your body wakes naturally). Why is this? Is there even any documented reasoning or is it just luck of the draw?
gpt
After a night's sleep, you've gone a longer than usual duration without eating food, drinking water, or moving.  Dehydration, low blood sugar, muscle soreness, or even substance withdrawals (caffeine, cannabis, etc) are almost universally the cause of the grumps.  Drink water, eat something, stretch, get your coffee.  You will feel *much* better.  This applies to moodiness during waking hours.  If something is making you mad, you're body is telling you it needs something, usually food or water.