シン, ね.る, ね.かす, い.ぬ, みたまや, や.める
lie down, sleep, rest, bed, remain unsold
JLPT3 G7 S13 F1034
The addition of 宀 roof/building to 侵 (deep) indicated a room crammed deep into the corner of a house. 寢 combines an abbreviated form# of this element + 爿 long, wooden sleeping pallet → *lie down*/*sleep* in a *back/inner room* → *lay down*; *go to bed*. Also, *leave* (unused).
[Full Kanji Etymology List]