Lack of sleep; insufficient sleep — a condition of not getting enough rest, often causing tiredness and reduced concentration.
昨夜は会議で遅くまで起きていたので、今日は寝不足だ。
I stayed up late for a meeting last night, so I'm sleep-deprived today.
寝不足のせいで集中力が続かない。
Because of lack of sleep, I can't maintain my concentration.
長期間の寝不足は健康に悪影響を与える。
Long-term sleep deprivation has negative effects on health.