I rarely sleep more than 4 hours a night during the week. Usually I get 3-4 hours, except for weekends, where I will sleep in and get a full 8+ hours of sleep.
I kind of forced myself to adjust to this schedule though, and now it seems normal, though at first was difficult. The body tends to like consistency, and will quickly learn a pattern of sleeping. If you deviate from it, like in your case, you will find that you have a hard time getting up, and not feel entirely rested.