While you might have the occasional all-nighter to finish an assignment, it is important to make sure you get your sleep. Almost all professors will give you more than enough time to do your assignments, assuming you start on time. Not sleeping will have a negative impact on the quality of your work and your ability to retain information; it can also lead to health issues. If you find you are not getting enough sleep, you should figure out whether you are overloading on classes or extracurriculars and what to cut back in. Even if you could manage everything in high school, college classes are often much more challenging or time consuming that high school classes were.