noun
stiff neck from sleeping wrong; kink in the neck
Refers specifically to neck pain or stiffness caused by sleeping in an awkward position. Often used in everyday conversation.
See also: 寝違え
朝起きたら寝違いで首が痛い。
I woke up with a stiff neck from sleeping wrong.
寝違いがひどくて、首を回せない。
My neck is so kinked I can't turn my head.
寝違え is a variant with the same meaning; both are commonly used, but 寝違い may be slightly more frequent in some regions.
Compound of 寝 (ne, 'sleep') and 違い (chigai, 'difference' or 'mistake'), literally 'sleep mistake', referring to the result of sleeping in a wrong position.