If you are getting drowsier on successive days, then you are getting less than your daily requirement and should add 15 to 30 minutes to your sleep time.

如果接连几天都感到瞌睡，那么，你就没有达到每天所需的睡眠量，应该再增加15到30分钟的睡眠时间。

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And the older children, questioned about their levels of tiredness, reported feeling much drowsier during mornings.

BBC: Children 'losing sleep over internet'