1To lie down or throw oneself down; to sprawl or lie on one's back (intransitive).
公園の芝生に寝転んで空を見た。
I lay down on the park grass and looked at the sky.
疲れてソファに寝転んだまま昼寝をしてしまった。
I was so tired that I flopped down on the sofa and took a nap.
赤ちゃんが床に寝転んで笑っている。
The baby is lying on the floor and laughing.