system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do our necks hurt all day after we sleep in an odd position, but the rest of our bodies can be in any position as we sleep and they do not get long lasting cramps?
gpt
Your neck is the most flexible part or your spinal column which is the boney part surrounding your spinal cord which is the nerves which report sensation and allow movement. 

Wait till you get older and have shoulders which have been injured in the past and scream bloody murder if you fall asleep in the wrong position. It is part of the joy of getting old. 

Until then it is possible to put your neck, containing the most vital part of your nervous system, in a bind while you sleep. Your neck muscles will complain the next day.