根据短文内容，用方框中所给单词的适当形式填空，每词限用一次。

Wake, quick, again, sleep, why

Dreams take up about one quarter of our ______ time. People have several dreams each night. Dreams are like short films. They are usually in color. Some dreams are like old films. They come to us over and over _______.
Sometimes we_______ up with a good feeling from a dream. But often we can’t remember the dream. Dreams can disappear(消失) _________from memory(记忆)
Too much dreaming can be harmful（有害的）. The more we sleep, the longer we dream. The mind is hard at work when we dream. That is _______ we may have a long sleep and still wake up tired.