深层睡眠 meaning in English

deep sleep

But , deep dreamless sleep would take you down to the lowest frequency , typically 2 to 3 cycles a second
但是无梦的深层睡眠将使你的脑电波频率降到最低，通常情况下为每秒2 3周。
In the fourth level ? the very deepest sleep ? brain waves are like calm ocean waves . . . long , slow , and rolling
在第四阶段，即最深层睡眠阶段，脑电波就像平静的海浪? ?长长地、缓慢地起伏波动。