小孩子经常打瞌睡，不是什么大事。
她看起来老是很累，上课的时候经常打瞌睡。
She looks tired all the time and keeps falling asleep in her classes.
同时，年纪大的人常常睡不沉，夜里时常醒来，这可能使他们白天经常打瞌睡的原因。
Also, older people often sleep less deeply and wake up more often throughout the night, which may be why they may nap more often during the daytime.
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