system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If the fetal position is such a natural sleeping position, why does slouching while sitting down negatively affect the spine over time?
gpt
The fetal position (recovery) is on ones side and is a laying posture. Gravity is effecting all of your body equally. 

Where as slouching the chair is taking the force of gravity off the shoulders and pelvis and your legs are being supported by the ground...

That leaves all 9.807 m/s² of gravity to affect your middle and lower spine in a way it was not designed for. Your spine being designed for pulling along the vertical rather than longitudinal axis.