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to sink (into)
to get depressed
ソファに沈み込んで寝た。
I sank into the sofa and slept.
古いソファに座ったら深く沈み込んだ。
When I sat on the old sofa, I sank deep into it.
重い荷物でタイヤが地面に沈み込んでいる。
The tires are sinking into the ground under the heavy load.