system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come when you do nothing all day you're more tired than when you're productive?
gpt
Hormones, or signals for your body, require a stimulus to be activated. The stimulus could be stress, fear, arousal, pain, motion, etc.

When you sit around and do nothing, your body senses that it does not need to be alert, so nothing is stimulated and you stay tired.

When you are actively engaged in doing something, your body becomes aware that you may need to be alert or ready for action, and it prompts you accordingly.