Video: Sleep is important. Have we made that clear yet, folks? In case you're still trying to put it off, this video shows what can start to happen the longer you go without sleep. Even after a single day, negative side effects like impaired focus and reduced ability to form memories can start setting in. The longer you go, the worse it gets. Your brain will eventually start forcing itself to go to sleep for brief periods at a time. Your body can become so stressed that your heart rate rises, or you start hallucinating.
Of course, your body isn't designed to naturally reach these stages alone. If you're trying to force yourself to stay awake for long periods of time, you should know that the risks aren't light. It only takes a few days without sleep for the side effects to become either directly or indirectly life-threatening.