1) hit the hay 去睡觉

I'm so sleepy. I'm gonna hit the hay. 我很累。我想去睡觉咯。。。

2) hit the sack 去睡觉

Ok guys! It's time to hit the sack! We have to get up early! 好吧！大家快去睡觉啦！我们明天很早要起床啊！

3) turn in 睡觉

I've been studying all day. My eyes are killing me. I think I'm gonna turn in now. 我看了一整天的书。我的眼睛很痛。我现在就想去睡觉咯。

4) go to bed/go to sleep 去睡觉

白洁! Why are you still awake?? 白洁为什么你还没睡觉！？I'm watching Gossip Girl online! 我在网上看 Gossip Girl！It's 3AM!! Go to bed!! 现在是早上三点啦！快去睡觉吧！