system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it that i need to crack my back and i don't feel normal until i do?
gpt
Bubbles! Bubbles always make people happy, right? In this case, there's oxygen, nitrogen, and carbon dioxide bubbles trapped in your joints that escape when you crack your back. These bubbles float away and relieve a bit of pressure build up, which also relaxes the things that hold your muscles in place, the ligaments, and the tight feeling, tension.

Most of it comes from the release of the body's natural little painkillers, endorphins, though. Your back might *actually* feel somewhat better, due to relief of pressure and loosening of the ligaments, but mostly it's the release of endorphins that block the pain signal to the brain. So you partially *really* feel better, and partially just *think* that you feel a bit better. Combined, you feel "normal" afterwards, but the effect will be temporary. Once it wears off, and some of the tension and pressure builds back up, you feel the need to pop it again.