A lack of sleep causes people to become more emotional. Or rather, it causes them to have less control of their emotions, so they'll swing into anger or sadness before they can reign in their feelings. I took two red eye flights under the same circumstances one year apart. I skied all day, had a few beers, ate a huge meal of Mexican food, and then sat on a plane not sleeping for five hours. The only thing that changed for me was what I had to do when I arrived home. The first year I laid on my bed and stared at the clock for four minutes before getting up to shower and go to work. Lack of sleep also helps strip things away. That was the day that I wrote an e-mail to a friend trying to explain the general feeling of what I do, rather than what I actually do. I said it's like sitting in front of a wall of electrical outlets and looking at a couple dozen extension cords. The goal is to plug and unplug all of the cords into the wall in a certain order. This process will take about 2 hours; the rest of the day is spent surfing the internet. It might not sound so bad on a normal day, but after not sleeping for 48 hours it will make you want to kill yourself. The morning after this red eye flight, thankfully did not contain any such revelations.