sleeping posture
Refers to the position or manner in which one sleeps, such as on one's back, side, or stomach.
His sleeping posture is always on his back.
寝様が悪いと、朝起きたときに体が痛くなる。
If your sleeping posture is bad, your body will ache when you wake up in the morning.
Formed from 寝 “sleeping” and 様 “appearance, manner,” with voicing of 様 to ざま.