To lie down (on one's side or back) to rest or sleep; to get into a reclining position. Often used for resting and not necessarily implying falling asleep.
毎朝ちょっと疲れたらソファに横になる。
When I'm a bit tired each morning, I lie down on the sofa.
病院で彼はベッドに横になって休んでいる。
In the hospital he is lying down on the bed and resting.
運動後はしばらく横になって体を休めてください。
After exercising, lie down for a while and rest your body.
赤ちゃんは眠くなると横になるとすぐ寝ることが多い。
Babies often fall asleep quickly when you lay them down.