翻译成睡眠模式的前三分之一 研究表明深睡状态只发生在这个时段
Sleep begins in stage one of the sleep phase known as NREM,or non-rapid eye movement,sleep.NREM sleep has four stages:light sleep,deeper sleep,and two stages of deepest sleep.and two stages of deepest sleep.Stage one is the "drifting off" period of light sleep in the transition between wakefulness and sleep and comprises about 5 percent of the entire sleep period.Stage two sleep involves a change in brain-wave patterns and increased resistance to arousal and accounts for 45–55 percent of total sleep time.Stages three and four are the deepest levels of sleep and occur only in the first third of the sleep period.NREM stage four sleep usually takes up 12 to 15 percent of total sleep time.Sleep terrors,sleep walking,and bedwetting episodes generally occur within stage four sleep or during partial arousals from this sleep stage.