system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do we sigh when we are sad?

As simple as that. Why do we sigh when we feel sad or melancholic?
gpt
When you take a deep breath, it stimulates your central nervous system in your chest and releases calming hormones.

This is also a reason why people feel relaxed when they smoke, they are doing deep breathing exercises.