I always sleep for more than eight hours during vacation time. However, during school days, I only sleep for four hours a day, which I think has repercussions in the long run.

The article below was taken from this site: http://www.umm.edu/sleep/normal_sleep.htm.
How Much Sleep Do I Need?

There is, in fact, a wide range of sleep time that is considered "normal." While the average normal amount of sleep is around 7.5 hours per night, there are some people who do just fine on 5 hours per night, and some who require as much as 9 hours per night. The key is to find the right amount for you. The best way to tell is by seeing how you function during the day.
For example, if after 6 hours of sleep you feel refreshed in the morning and awake during your daylight hours, then you don't need more than that. If, on the other hand, you need 9 hours a night to feel refreshed and to function well during the day, then that is what your individual requirement is and sleeping the "normal" amount of 7.5 hours per night will actually leave you sleep deprived.
If you are getting what you consider to be an adequate amount of sleep and are still unrefeshed and sleepy, then you might have an organic sleep disorder and should consider seeking professional consultation.

How about you? How many hours do you sleep everyday?