system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:When getting a cramp why is your first instinct to become motionless and why does it hurt when you move.
gpt
This might not sound useful, but...

> When getting a cramp why is your first instinct to become motionless 

because it

> it hurt[s] when you move.

A cramp is muscles literally cramping (for various reasons) beyond they ability to be healthy, the body tells you about the "danger!" as "pain". As the body tries to limit the possible "damage" in the face of that danger, it just attempts to stop whatever it was doing with that limb to just keep that obviously (at the moment) faulty muscle alone.