system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why we feel refreshed after a workout, but feel tired after a work day at office?
gpt
Exercise releases chemicals called endorphins which "trick" your body into feeling less pain and gives you a positive feeling.  If you feel like crap after a day of sitting at the office it's most likely due to mental fatigue or food you've eaten.  When you are not moving your body slows down your calorie burning rate so you're going to get less energy from the food you eat.  Try moving around more and stay hydrated.