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to fall fast asleep
to be confined to one's bed; to be laid up
風邪をひいて二日間寝込んだ。
I caught a cold and was laid up in bed for two days.
祖父は先月から腰を悪くして寝込んでいる。
My grandfather has been laid up in bed since last month with a bad back.
過労で寝込む前に無理を早めにやめるべきだった。
I should have stopped pushing myself sooner before being laid low by overwork.