One important concept that I am interested in is circadian rhythm, which is a 24-hour cycle that rules all organism, including human being. There are many types of circadian rhythm sleep disorder, and delayed sleep-phase syndrome (DSPS) is one type of them. As a college student, I have gone through somewhat mild DSPS. People with DSPS generally fall asleep at almost the same time after midnight and have difficulty waking up in the morning.
One of my friends has been in a strong disorder for a long time. She usually goes to bed at 3:00 in the morning and gets up around 5:00 in the afternoon. She tried to go back to the normal life, but she found that it was more difficult than what she expected. Gradually no one invited her to take part in social activities any more; in some extent, she became isolated.
Sometimes people may not pay attention to this common problem, whose prevalence was calculated to be 0.17%, according to a nationwide epidemiological study performed in Norway (1). However, it is an invisible disability. Patients with it have trouble both in their daily social life. It has been referred as "social jet lag" and here is a video about this. Keeping life in a normal cycle is crucial for everyone because abnormal circadian rhythms have been associated with depression, bipolar disorder and seasonal affective disorder, etc.
After knowing this, I think, in order to keep healthy, I will not delay my sleep any more, even before midterm seasons.