system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Mechanically, what is happening in your body to give you a stiff neck on one side after sleeping in a bad position?

Every so often I will wake up like this. Why is it that when I turn or tilt my head to one side, I feel like I can't move it and I experience a lot of pain? Is something getting in the way or is it just muscle that doesn't want to move anymore?
gpt
Sleeping in a bad position can physically strain either muscles or other soft tissue in your neck, causing microscopic damage which in turn causes inflammation which in turn puts pressure on nerves and causes pain. This is working as intended as your body is signalling you to not cause further damage by moving your neck in certain ways while its busy with the repairs.

A latex rubber band serves as a good analogy - stretch it out and keep it stretched for a long period of time, once released from the stretching it is unable to return to its original length because even though nothing visible has happened to it, there is microscopic damage - you sprained your rubber band!

Fortunately our bodies are very good at dealing with light tissue damage like that, it is in fact used as a catalyst for growth in some cases and no cause for concern.

Eating a varied diet with lots of nutrients and keeping active physically make your body more flexible and thus more resistant to this kind of damage.