Lack of sleep causes weight gain by making us feeling hungry all day long as a result of elevated hormone ghrelin. Unfortunately it also causes us wanting to eat more high carb, high calorie foods, which are not the most nutritious ones.
We also experience more emotional disturbances and we react inappropriate ways. In other words even those emotions are more primitive causing us even more trouble. We also have a tendency to overreact.
It can make us forgetful. It has been proven from time to time that lack of sleep seriously impair our cognitive abilities. We are just unable to think clearly, have trouble remembering things, we have trouble concentrating and have difficulties learning.
Impair the immune system: we not only catch cold more easily, but getting out of it takes much longer as well. But our immune systems is not only responsible for repelling cold, it has a wide range of functions to protect our body so a weak immune system is not something we want to have.
It also impacts our motor skills: in other words we are just somehow more clumsy than normal. Our reflexes are slower and our depth perception gets worse.
It increases the stress hormone cortisol, making us more irritable in general.
And finally we experience lower sex drive. Nothing more to add.
Original article can be found here: http://www.huffingtonpost.com/2014/09/18/scary-sleep-deprivation-effects_n_2807026.html?slideshow=true#gallery/255140/0