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.
2. I’m so tired that I could sleep for a whole day.
3. He likes to sleep for an hour in the afternoon.
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.
2. I haven’t had enough sleep lately.
3. I didn’t get much sleep last night.
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.
2. He fell asleep while he was reading a book.
3. The man sitting in front of me is asleep.
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)