Sleep tight （informal）used especially to children before they go to bed to say that you hope they sleep well.
（尤用以打发孩子睡觉）睡个好觉
hit the hay
hit the sack
to go to bed 上床睡觉
I am gonna hit the hay.
sleep like a log
sleep like a baby
沉睡，酣睡
lie in=sleep in: to stay in bed after the time you usually get up 睡懒觉;起得晚
Did you sleep in this morning?
It's a holiday tomorrow, so you can lie in. 明天放假，你可以睡懒觉了。
sleep on sth: to delay making a decision about sth until the next day, so that you have time to think about it
把...留待第二天决定；把..拖延到第二天再说
比如，你朋友挖你一起创业，创办小紫美语，你说：
Could I sleep on it and let you know tomorrow?
sleep over： to stay the night at sb else's home 在别人家里过夜
你去你闺蜜家参加party，太晚了，闺蜜和你说：
It's very late now. Why don't you sleep over?
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