Loss of sleep is cumulative. After 3 days, you might think you're getting by fine on 4 hours of sleep per night, but it's catching up to you. You start saying

Loss of sleep is cumulative. After 3 days, you might think you're getting by fine on 4 hours of sleep per night, but it's catching up to you. You start saying things that don't make sense, or pausing inexplicably during conversations. You start zoning out when reading, and make decisions based on habit rather than logic. Small inconveniences start making you angry, and complex problems are baffling. Organization becomes impossible. Your muscles are weak and uncoordinated, you bump into things like you're drunk. You'll begin to stop caring, you'll stop enjoying things. Over time, it just gets worse and worse, until you actually start hallucinating. Adrenaline can get you through some difficult situations, but in the long run health problems will catch up to you.