noun
sleeping posture
Refers to the position or manner in which one sleeps, such as on one's back, side, or stomach.
彼の寝様はいつも仰向けだ。
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.