1
kotatsu;table over an electric heater, with a hanging quilt to retain heat (orig. over a charcoal brazier in a floor well)
こたつで寝ちゃったら風邪引くのはあたりまえ。自己管理がなっていない。
Of course you'll catch a cold if you fall asleep under the kotatsu. You have to learn to take care of yourself.
Other forms
火燵 【こたつ】 (rarely used kanji form)