Sleep
to rest with your eyes closed and your mind and body not active 睡觉，入睡 [不及物动词]
1. They all went to sleep except me.
除我之外，他们都去睡觉了。
2. Im so tired that I could sleep for a whole day.
我真是累极了，简直可以睡上一整天。
3. He likes to sleep for an hour in the afternoon.
他喜欢在下午睡一小时觉。
the natural state of rest in which your eyes are closed, your body is not active, and your mind is not conscious 睡觉，睡眠 [不可数名词]
1. I need to get some sleep.
我得睡一会儿。
2. I havent had enough sleep lately.
最近我睡眠不足。
3. I didnt get much sleep last night.
昨晚我睡得不好。
Asleep
in a state of sleep; sleeping 睡着的 [不可置于名词前]
1. Because I am tired, I fall asleep quickly.
因为我很疲劳，因此很快就睡着了。
2. He fell asleep while he was reading a book.
他在读书的时候睡着了。
3. The man sitting in front of me is asleep.
坐在我前面的人在睡觉。
【注意】
1. sleep可以用作动词和名词。用作动词意为睡觉，入睡，为不及物动词。用作名词意为睡觉，睡眠，为不可数名词。
2. asleep和awake为一组反义词，用作形容词时，不可置于名词前。
3. a- 作为前缀可以改变词根的词性。
a + sleep(名词/动词) asleep(形容词)
a + wake(名词/动词) awake(形容词)