Delayed Sleep-Phase Syndrome (DSPS) is a circadian rhythm sleep disorder in which the individual's internal body clock is delayed with respect to the typical sleep at night, rise in the morning pattern of most adults. Such people are sometimes called "night owls", though for those with DSPS, their hours are not by choice.
睡眠相位延迟综合症(Delayed Sleep-Phase Syndrome，简写为DSPS)是一种生物周期性睡眠紊乱症，指一些人体内的生物钟比通常意义上的“晚上睡觉，早上起床”这种模式有所延迟。这些人一般被称为“夜猫子”，不过对这些患有睡眠相位延迟综合症的人来说，这样的作息时间并不是他们自己选择的。
People with DSPS generally fall asleep late at night, often in the pre-dawn hours, and wake in the late morning or in the afternoon. Furthermore, there is a striking inability to fall asleep at an earlier, more typical bedtime. As a result, many people with DSPS have been labelled as insomniacs. But if such a person is allowed to follow his internal sleep pattern, he generally has no problems with either falling asleep or waking naturally.
However, if he ignores his internal clock and attempts to live on a normal schedule, DSPS can cause difficulty thinking clearly, driving safely, and generally functioning well. Over time, this may significantly reduce a person's productivity and enjoyment of life, and can lead to clinical depression or other stress-related medical problems.