Okay, the side effects of lack of sleep are mental and physical. Physically, you can appear almost drunk after a short period of time between 12 to 48 hours of lack of sleep. You lose dexterity, you lose emotional and mental clarity, you can't speak correctly, your ability to respond to things is slowed down immeasurably, you can have actual physical symptoms such as chronic fatigue syndrome, which actually affects more women than men between the ages of 40 and 50. You can have anything from symptoms of a cold, to muscle aches, joint aches, the inability to remember things, high irritability, so that little things will set you off which normally would be no big deal to you. You also have a very low resistance to any kinds of colds or infections, you can't recuperate from them as quickly either. If you get too exhausted, you will actually continue the syndrome to the point where you will get infections that you can't get rid of it all. Some people say that, you can develop cancer, diabetes, high blood pressure, all sorts of things. It also sets you off for the inability to eat properly, so that you're constantly picking things like caffeine or sugar that your body can't process, and you are in fight or flight symptom all the time. So, your body never really gets downtime to recuperate and feel better basically. So, that you will not be able to function on a normal level.