Then you get successively deeper, II through IV, slow, irregular, high amplitude delta waves, and then once you reach stage IV you start going up again, up through stage III and II.

然后睡得越来越深，从第二到第四阶段，慢，不规则，高振幅的δ波，等你到达第四阶段，你又开始返回，第三阶段和第二阶段。

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